rustpython-vm 0.6.0

use self::types::{PyBaseException, PyBaseExceptionRef, PyException, PyMemoryError};
pub use super::exception_group::exception_group;
use crate::common::lock::PyRwLock;
use crate::object::{Traverse, TraverseFn};
use crate::{
    AsObject, Context, Py, PyObject, PyObjectRef, PyPayload, PyRef, PyResult, TryFromObject,
    VirtualMachine,
    builtins::{
        PyList, PyNone, PyStr, PyStrRef, PyTuple, PyTupleRef, PyType, PyTypeRef,
        traceback::{PyTraceback, PyTracebackRef},
    },
    class::{PyClassImpl, StaticType},
    convert::{IntoPyException, ToPyException, ToPyObject},
    function::{ArgIterable, FuncArgs, IntoFuncArgs, PySetterValue},
    py_io::{self, Write},
    stdlib::sys,
    suggestion::offer_suggestions,
    types::{Callable, Constructor, Initializer, Representable},
};
use core::fmt::{self, Display, Formatter};
use core::sync::atomic::{AtomicBool, Ordering};
use itertools::Itertools;
#[cfg(feature = "host_env")]
use std::io::{BufRead, BufReader};
use std::sync::Mutex;
use std::{collections::HashSet, io};

unsafe impl Traverse for PyBaseException {
    fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
        self.traceback.traverse(tracer_fn);
        self.cause.traverse(tracer_fn);
        self.context.traverse(tracer_fn);
        self.args.traverse(tracer_fn);
    }
}

impl core::fmt::Debug for PyBaseException {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        // TODO: implement more detailed, non-recursive Debug formatter
        f.write_str("PyBaseException")
    }
}

const MEMORY_ERROR_FREELIST_SIZE: usize = 16;

struct MemoryErrorHusk(*mut PyObject);
unsafe impl Send for MemoryErrorHusk {}

static MEMORY_ERROR_FREELIST: Mutex<[Option<MemoryErrorHusk>; MEMORY_ERROR_FREELIST_SIZE]> =
    Mutex::new([const { None }; MEMORY_ERROR_FREELIST_SIZE]);

impl PyPayload for PyBaseException {
    #[inline]
    fn class(ctx: &Context) -> &'static Py<PyType> {
        ctx.exceptions.base_exception_type
    }
}

impl PyPayload for PyMemoryError {
    const PAYLOAD_TYPE_ID: core::any::TypeId = <PyException as PyPayload>::PAYLOAD_TYPE_ID;
    const HAS_FREELIST: bool = true;
    const MAX_FREELIST: usize = MEMORY_ERROR_FREELIST_SIZE;

    #[inline]
    unsafe fn validate_downcastable_from(obj: &PyObject) -> bool {
        obj.class()
            .fast_issubclass(<Self as StaticType>::static_type())
    }

    fn class(_ctx: &Context) -> &'static Py<PyType> {
        <Self as StaticType>::static_type()
    }

    unsafe fn freelist_push(obj: *mut PyObject) -> bool {
        let Ok(mut list) = MEMORY_ERROR_FREELIST.lock() else {
            return false;
        };
        match list.iter_mut().find(|element| element.is_none()) {
            Some(element) => {
                *element = Some(MemoryErrorHusk(obj));
                true
            }
            None => false,
        }
    }

    unsafe fn freelist_pop(_payload: &Self) -> Option<core::ptr::NonNull<PyObject>> {
        let husk = MEMORY_ERROR_FREELIST
            .lock()
            .ok()?
            .iter_mut()
            .find_map(|element| element.take())?;
        core::ptr::NonNull::new(husk.0)
    }
}

impl VirtualMachine {
    // Why `impl VirtualMachine`?
    // These functions are natively free function in CPython - not methods of PyException

    /// Print exception chain by calling sys.excepthook
    pub fn print_exception(&self, exc: &Py<PyBaseException>) {
        let vm = self;
        let write_fallback = |exc, errstr| {
            if let Ok(stderr) = sys::get_stderr(vm) {
                let mut stderr = py_io::PyWriter(stderr, vm);
                // if this fails stderr might be closed -- ignore it
                let _ = writeln!(stderr, "{errstr}");
                let _ = self.write_exception(&mut stderr, exc);
            } else {
                eprintln!("{errstr}\nlost sys.stderr");
                let _ = self.write_exception(&mut py_io::IoWriter(io::stderr()), exc);
            }
        };
        if let Ok(excepthook) = vm.sys_module.get_attr("excepthook", vm) {
            let (exc_type, exc_val, exc_tb) = vm.split_exception(exc.to_owned());
            if let Err(eh_exc) = excepthook.call((exc_type, exc_val, exc_tb), vm) {
                write_fallback(&eh_exc, "Error in sys.excepthook:");
                write_fallback(exc, "Original exception was:");
            }
        } else {
            write_fallback(exc, "missing sys.excepthook");
        }
    }

    pub fn write_exception<W: Write>(
        &self,
        output: &mut W,
        exc: &Py<PyBaseException>,
    ) -> Result<(), W::Error> {
        let seen = &mut HashSet::<usize>::new();
        self.write_exception_recursive(output, exc, seen)
    }

    fn write_exception_recursive<W: Write>(
        &self,
        output: &mut W,
        exc: &Py<PyBaseException>,
        seen: &mut HashSet<usize>,
    ) -> Result<(), W::Error> {
        // This function should not be called directly,
        // use `wite_exception` as a public interface.
        // It is similar to `print_exception_recursive` from `CPython`.
        seen.insert(exc.get_id());

        #[allow(clippy::manual_map)]
        if let Some((cause_or_context, msg)) = if let Some(cause) = exc.__cause__() {
            // This can be a special case: `raise e from e`,
            // we just ignore it and treat like `raise e` without any extra steps.
            Some((
                cause,
                "\nThe above exception was the direct cause of the following exception:\n",
            ))
        } else if let Some(context) = exc.__context__() {
            // This can be a special case:
            //   e = ValueError('e')
            //   e.__context__ = e
            // In this case, we just ignore
            // `__context__` part from going into recursion.
            Some((
                context,
                "\nDuring handling of the above exception, another exception occurred:\n",
            ))
        } else {
            None
        } {
            if !seen.contains(&cause_or_context.get_id()) {
                self.write_exception_recursive(output, &cause_or_context, seen)?;
                writeln!(output, "{msg}")?;
            } else {
                seen.insert(cause_or_context.get_id());
            }
        }

        self.write_exception_inner(output, exc)
    }

    /// Print exception with traceback
    pub fn write_exception_inner<W: Write>(
        &self,
        output: &mut W,
        exc: &Py<PyBaseException>,
    ) -> Result<(), W::Error> {
        let vm = self;

        let traceback = exc.traceback.read().clone();
        if let Some(tb) = traceback {
            writeln!(output, "Traceback (most recent call last):")?;
            for tb in tb.iter() {
                write_traceback_entry(output, &tb)?;
            }
        }

        let varargs = exc.args();
        let args_repr = vm.exception_args_as_string(&varargs, true);

        let exc_class = exc.class();

        if exc_class.fast_issubclass(vm.ctx.exceptions.syntax_error) {
            return self.write_syntaxerror(output, exc, exc_class, &args_repr);
        }

        let exc_name = exc_class.name();
        match args_repr.len() {
            0 => write!(output, "{exc_name}"),
            1 => write!(output, "{}: {}", exc_name, args_repr[0]),
            _ => write!(
                output,
                "{}: ({})",
                exc_name,
                args_repr.into_iter().format(", "),
            ),
        }?;

        if let Some(suggestions) = offer_suggestions(exc, vm) {
            writeln!(output, ". Did you mean: '{suggestions}'?")
        } else {
            writeln!(output)
        }
    }

    /// Format and write a SyntaxError
    /// This logic is derived from TracebackException._format_syntax_error
    ///
    /// The logic has support for `end_offset` to highlight a range in the source code,
    /// but it looks like `end_offset` is not used yet when SyntaxErrors are created.
    fn write_syntaxerror<W: Write>(
        &self,
        output: &mut W,
        exc: &Py<PyBaseException>,
        exc_type: &Py<PyType>,
        args_repr: &[PyRef<PyStr>],
    ) -> Result<(), W::Error> {
        let vm = self;
        debug_assert!(exc_type.fast_issubclass(vm.ctx.exceptions.syntax_error));

        let getattr = |attr: &'static str| exc.as_object().get_attr(attr, vm).ok();

        let maybe_lineno = getattr("lineno").map(|obj| {
            obj.str(vm)
                .unwrap_or_else(|_| vm.ctx.new_str("<lineno str() failed>"))
        });
        let maybe_filename = getattr("filename").and_then(|obj| obj.str(vm).ok());

        let maybe_text = getattr("text").map(|obj| {
            obj.str(vm)
                .unwrap_or_else(|_| vm.ctx.new_str("<text str() failed>"))
        });

        let mut filename_suffix = String::new();

        if let Some(lineno) = maybe_lineno {
            let filename = match maybe_filename {
                Some(filename) => filename,
                None => vm.ctx.new_str("<string>"),
            };
            writeln!(output, r##"  File "{filename}", line {lineno}"##,)?;
        } else if let Some(filename) = maybe_filename {
            filename_suffix = format!(" ({filename})");
        }

        if let Some(text) = maybe_text {
            // if text ends with \n or \r\n, remove it
            use rustpython_common::wtf8::CodePoint;
            let text_wtf8 = text.as_wtf8();
            let r_text = text_wtf8.trim_end_matches(|cp: CodePoint| {
                cp == CodePoint::from_char('\n') || cp == CodePoint::from_char('\r')
            });
            let l_text = r_text.trim_start_matches(|cp: CodePoint| {
                cp == CodePoint::from_char(' ')
                    || cp == CodePoint::from_char('\n')
                    || cp == CodePoint::from_char('\x0c') // \f
            });
            let spaces = (r_text.len() - l_text.len()) as isize;

            writeln!(output, "    {l_text}")?;

            let maybe_offset: Option<isize> =
                getattr("offset").and_then(|obj| obj.try_to_value::<isize>(vm).ok());

            if let Some(offset) = maybe_offset {
                let maybe_end_offset: Option<isize> =
                    getattr("end_offset").and_then(|obj| obj.try_to_value::<isize>(vm).ok());
                let maybe_end_lineno: Option<isize> =
                    getattr("end_lineno").and_then(|obj| obj.try_to_value::<isize>(vm).ok());
                let maybe_lineno_int: Option<isize> =
                    getattr("lineno").and_then(|obj| obj.try_to_value::<isize>(vm).ok());

                // Only show caret if end_lineno is same as lineno (or not set)
                let same_line = match (maybe_lineno_int, maybe_end_lineno) {
                    (Some(lineno), Some(end_lineno)) => lineno == end_lineno,
                    _ => true,
                };

                // A lone continuation at EOF has no highlighted source span.
                let lone_line_continuation =
                    maybe_end_offset == Some(-1) && l_text.to_string_lossy() == "\\";

                if same_line && !lone_line_continuation {
                    let mut end_offset = match maybe_end_offset {
                        Some(0) | None => offset,
                        Some(end_offset) => end_offset,
                    };

                    if offset == end_offset || end_offset == -1 {
                        end_offset = offset + 1;
                    }

                    // Convert 1-based column offset to 0-based index into stripped text
                    let colno = offset - 1 - spaces;
                    let end_colno = end_offset - 1 - spaces;
                    if colno >= 0 {
                        let caret_space = l_text
                            .code_points()
                            .take(colno as usize)
                            .map(|cp| cp.to_char().filter(|c| c.is_whitespace()).unwrap_or(' '))
                            .collect::<String>();

                        let mut error_width = end_colno - colno;
                        if error_width < 1 {
                            error_width = 1;
                        }

                        writeln!(
                            output,
                            "    {}{}",
                            caret_space,
                            "^".repeat(error_width as usize)
                        )?;
                    }
                }
            }
        }

        let exc_name = exc_type.name();

        match args_repr.len() {
            0 => write!(output, "{exc_name}{filename_suffix}"),
            1 => write!(output, "{}: {}{}", exc_name, args_repr[0], filename_suffix),
            _ => write!(
                output,
                "{}: ({}){}",
                exc_name,
                args_repr.iter().format(", "),
                filename_suffix
            ),
        }?;

        match offer_suggestions(exc, vm) {
            Some(suggestions) => writeln!(output, ". Did you mean: '{suggestions}'?"),
            None => writeln!(output),
        }
    }

    fn exception_args_as_string(&self, varargs: &Py<PyTuple>, str_single: bool) -> Vec<PyStrRef> {
        let vm = self;
        match varargs.as_slice().len() {
            0 => vec![],
            1 => {
                let args0_repr = if str_single {
                    varargs.as_slice()[0]
                        .str(vm)
                        .unwrap_or_else(|_| PyStr::from("<element str() failed>").into_ref(&vm.ctx))
                } else {
                    varargs.as_slice()[0].repr(vm).unwrap_or_else(|_| {
                        PyStr::from("<element repr() failed>").into_ref(&vm.ctx)
                    })
                };
                vec![args0_repr]
            }
            _ => varargs
                .as_slice()
                .iter()
                .map(|vararg| {
                    vararg.repr(vm).unwrap_or_else(|_| {
                        PyStr::from("<element repr() failed>").into_ref(&vm.ctx)
                    })
                })
                .collect(),
        }
    }

    pub fn split_exception(
        &self,
        exc: PyBaseExceptionRef,
    ) -> (PyObjectRef, PyObjectRef, PyObjectRef) {
        let tb = exc.traceback().to_pyobject(self);
        let class = exc.class().to_owned();
        (class.into(), exc.into(), tb)
    }

    /// Similar to PyErr_NormalizeException in CPython
    pub fn normalize_exception(
        &self,
        exc_type: PyObjectRef,
        exc_val: PyObjectRef,
        exc_tb: PyObjectRef,
    ) -> PyResult<PyBaseExceptionRef> {
        let ctor = ExceptionCtor::try_from_object(self, exc_type)?;
        let exc = ctor.instantiate_value(exc_val, self)?;
        if let Some(tb) = Option::<PyTracebackRef>::try_from_object(self, exc_tb)? {
            exc.set_traceback(Some(tb));
        }
        Ok(exc)
    }

    pub fn invoke_exception(
        &self,
        cls: &Py<PyType>,
        args: Vec<PyObjectRef>,
    ) -> PyResult<PyBaseExceptionRef> {
        // TODO: fast-path built-in exceptions by directly instantiating them? Is that really worth it?
        let res = PyType::call(cls, args.into_args(self), self)?;
        res.downcast::<PyBaseException>().map_err(|obj| {
            self.new_type_error(format!(
                "calling {} should have returned an instance of BaseException, not {}",
                cls,
                obj.class()
            ))
        })
    }
}

#[cfg(feature = "host_env")]
fn print_source_line<W: Write>(
    output: &mut W,
    filename: &str,
    lineno: usize,
) -> Result<(), W::Error> {
    // TODO: use io.open() method instead, when available, according to https://github.com/python/cpython/blob/main/Python/traceback.c#L393
    // TODO: support different encodings
    let file = match crate::host_env::fs::open(filename) {
        Ok(file) => file,
        Err(_) => return Ok(()),
    };
    let file = BufReader::new(file);

    for (i, line) in file.lines().enumerate() {
        if i + 1 == lineno {
            if let Ok(line) = line {
                // Indented with 4 spaces
                writeln!(output, "    {}", line.trim_start())?;
            }
            return Ok(());
        }
    }

    Ok(())
}

/// Print exception occurrence location from traceback element
fn write_traceback_entry<W: Write>(
    output: &mut W,
    tb_entry: &Py<PyTraceback>,
) -> Result<(), W::Error> {
    let filename = tb_entry.frame.iframe().code().source_path().as_str();
    writeln!(
        output,
        r##"  File "{}", line {}, in {}"##,
        filename.trim_start_matches(r"\\?\"),
        tb_entry.lineno,
        tb_entry.frame.iframe().code().obj_name
    )?;

    #[cfg(feature = "host_env")]
    print_source_line(output, filename, tb_entry.lineno.get())?;

    Ok(())
}

#[derive(Clone)]
pub enum ExceptionCtor {
    Class(PyTypeRef),
    Instance(PyBaseExceptionRef),
}

impl TryFromObject for ExceptionCtor {
    fn try_from_object(vm: &VirtualMachine, obj: PyObjectRef) -> PyResult<Self> {
        obj.downcast::<PyType>()
            .and_then(|cls| {
                if cls.fast_issubclass(vm.ctx.exceptions.base_exception_type) {
                    Ok(Self::Class(cls))
                } else {
                    Err(cls.into())
                }
            })
            .or_else(|obj| obj.downcast::<PyBaseException>().map(Self::Instance))
            .map_err(|obj| {
                vm.new_type_error(format!(
                    "exceptions must be classes or instances deriving from BaseException, not {}",
                    obj.class().name()
                ))
            })
    }
}

impl ExceptionCtor {
    pub fn instantiate(self, vm: &VirtualMachine) -> PyResult<PyBaseExceptionRef> {
        match self {
            Self::Class(cls) => vm.invoke_exception(&cls, vec![]),
            Self::Instance(exc) => Ok(exc),
        }
    }

    pub fn instantiate_value(
        self,
        value: PyObjectRef,
        vm: &VirtualMachine,
    ) -> PyResult<PyBaseExceptionRef> {
        let exc_inst = value.clone().downcast::<PyBaseException>().ok();
        match (self, exc_inst) {
            // both are instances; which would we choose?
            (Self::Instance(_exc_a), Some(_exc_b)) => {
                Err(vm.new_type_error("instance exception may not have a separate value"))
            }
            // if the "type" is an instance and the value isn't, use the "type"
            (Self::Instance(exc), None) => Ok(exc),
            // if the value is an instance of the type, use the instance value
            (Self::Class(cls), Some(exc)) if exc.fast_isinstance(&cls) => Ok(exc),
            // otherwise; construct an exception of the type using the value as args
            (Self::Class(cls), _) => {
                let args = match_class!(match value {
                    PyNone => vec![],
                    tup @ PyTuple => tup.as_slice().to_vec(),
                    exc @ PyBaseException => exc.args().as_slice().to_vec(),
                    obj => vec![obj],
                });
                vm.invoke_exception(&cls, args)
            }
        }
    }
}

#[derive(Debug)]
pub struct ExceptionZoo {
    pub base_exception_type: &'static Py<PyType>,
    pub base_exception_group: &'static Py<PyType>,
    pub system_exit: &'static Py<PyType>,
    pub keyboard_interrupt: &'static Py<PyType>,
    pub generator_exit: &'static Py<PyType>,
    pub exception_type: &'static Py<PyType>,
    pub stop_iteration: &'static Py<PyType>,
    pub stop_async_iteration: &'static Py<PyType>,
    pub arithmetic_error: &'static Py<PyType>,
    pub floating_point_error: &'static Py<PyType>,
    pub overflow_error: &'static Py<PyType>,
    pub zero_division_error: &'static Py<PyType>,
    pub assertion_error: &'static Py<PyType>,
    pub attribute_error: &'static Py<PyType>,
    pub buffer_error: &'static Py<PyType>,
    pub eof_error: &'static Py<PyType>,
    pub import_error: &'static Py<PyType>,
    pub module_not_found_error: &'static Py<PyType>,
    pub lookup_error: &'static Py<PyType>,
    pub index_error: &'static Py<PyType>,
    pub key_error: &'static Py<PyType>,
    pub memory_error: &'static Py<PyType>,
    pub name_error: &'static Py<PyType>,
    pub unbound_local_error: &'static Py<PyType>,
    pub os_error: &'static Py<PyType>,
    pub blocking_io_error: &'static Py<PyType>,
    pub child_process_error: &'static Py<PyType>,
    pub connection_error: &'static Py<PyType>,
    pub broken_pipe_error: &'static Py<PyType>,
    pub connection_aborted_error: &'static Py<PyType>,
    pub connection_refused_error: &'static Py<PyType>,
    pub connection_reset_error: &'static Py<PyType>,
    pub file_exists_error: &'static Py<PyType>,
    pub file_not_found_error: &'static Py<PyType>,
    pub interrupted_error: &'static Py<PyType>,
    pub is_a_directory_error: &'static Py<PyType>,
    pub not_a_directory_error: &'static Py<PyType>,
    pub permission_error: &'static Py<PyType>,
    pub process_lookup_error: &'static Py<PyType>,
    pub timeout_error: &'static Py<PyType>,
    pub reference_error: &'static Py<PyType>,
    pub runtime_error: &'static Py<PyType>,
    pub not_implemented_error: &'static Py<PyType>,
    pub recursion_error: &'static Py<PyType>,
    pub python_finalization_error: &'static Py<PyType>,
    pub syntax_error: &'static Py<PyType>,
    pub incomplete_input_error: &'static Py<PyType>,
    pub indentation_error: &'static Py<PyType>,
    pub tab_error: &'static Py<PyType>,
    pub system_error: &'static Py<PyType>,
    pub type_error: &'static Py<PyType>,
    pub value_error: &'static Py<PyType>,
    pub unicode_error: &'static Py<PyType>,
    pub unicode_decode_error: &'static Py<PyType>,
    pub unicode_encode_error: &'static Py<PyType>,
    pub unicode_translate_error: &'static Py<PyType>,

    #[cfg(feature = "jit")]
    pub jit_error: &'static Py<PyType>,

    pub warning: &'static Py<PyType>,
    pub deprecation_warning: &'static Py<PyType>,
    pub pending_deprecation_warning: &'static Py<PyType>,
    pub runtime_warning: &'static Py<PyType>,
    pub syntax_warning: &'static Py<PyType>,
    pub user_warning: &'static Py<PyType>,
    pub future_warning: &'static Py<PyType>,
    pub import_warning: &'static Py<PyType>,
    pub unicode_warning: &'static Py<PyType>,
    pub bytes_warning: &'static Py<PyType>,
    pub resource_warning: &'static Py<PyType>,
    pub encoding_warning: &'static Py<PyType>,
}

macro_rules! extend_exception {
    (
        $exc_struct:ident,
        $ctx:expr,
        $class:expr
    ) => {
        extend_exception!($exc_struct, $ctx, $class, {});
    };
    (
        $exc_struct:ident,
        $ctx:expr,
        $class:expr,
        { $($name:expr => $value:expr),* $(,)* }
    ) => {
        $exc_struct::extend_class($ctx, $class);
        extend_class!($ctx, $class, {
            $($name => $value,)*
        });
    };
}

impl PyBaseException {
    pub(crate) fn new(args: Vec<PyObjectRef>, vm: &VirtualMachine) -> Self {
        Self {
            traceback: PyRwLock::new(None),
            cause: PyRwLock::new(None),
            context: PyRwLock::new(None),
            suppress_context: AtomicBool::new(false),
            args: PyRwLock::new(PyTuple::new_ref(args, &vm.ctx)),
        }
    }

    pub fn get_arg(&self, idx: usize) -> Option<PyObjectRef> {
        self.args.read().as_slice().get(idx).cloned()
    }
}

impl PyBaseException {
    pub fn set_traceback(&self, traceback: Option<PyTracebackRef>) {
        *self.traceback.write() = traceback;
    }

    pub fn set_cause(&self, cause: Option<PyRef<Self>>) {
        let mut c = self.cause.write();
        self.set_suppress_context(true);
        *c = cause;
    }

    pub fn set_context(&self, context: Option<PyRef<Self>>) {
        *self.context.write() = context;
    }

    pub(super) fn __suppress_context__(&self) -> bool {
        self.suppress_context.load(Ordering::Relaxed)
    }

    pub(super) fn set_suppress_context(&self, suppress_context: bool) {
        self.suppress_context
            .store(suppress_context, Ordering::Relaxed);
    }

    pub fn args(&self) -> PyTupleRef {
        self.args.read().clone()
    }
    pub fn __traceback__(&self) -> Option<PyTracebackRef> {
        self.traceback.read().clone()
    }
    pub fn __cause__(&self) -> Option<PyRef<Self>> {
        self.cause.read().clone()
    }
    pub fn __context__(&self) -> Option<PyRef<Self>> {
        self.context.read().clone()
    }
}

#[pyclass(
    with(Py, PyRef, Constructor, Initializer, Representable),
    flags(BASETYPE, HAS_DICT)
)]
impl PyBaseException {}

#[pyclass]
impl Py<PyBaseException> {
    #[inline]
    pub fn traceback(&self) -> Option<PyTracebackRef> {
        self.__traceback__()
    }

    #[pymethod]
    pub(super) fn __str__(&self, vm: &VirtualMachine) -> PyStrRef {
        let str_args = vm.exception_args_as_string(&self.args(), true);
        match str_args.into_iter().exactly_one() {
            Err(i) if i.len() == 0 => vm.ctx.empty_str.to_owned(),
            Ok(s) => s,
            Err(i) => PyStr::from(format!("({})", i.format(", "))).into_ref(&vm.ctx),
        }
    }

    #[pymethod]
    pub fn add_note(&self, note: PyStrRef, vm: &VirtualMachine) -> PyResult<()> {
        let dict = crate::builtins::object::object_get_dict(self.as_object().to_owned(), vm)
            .map_err(|_| vm.new_attribute_error("Exception object has no __dict__"))?;

        let notes = if let Ok(notes) = dict.get_item("__notes__", vm) {
            notes
        } else {
            let new_notes = vm.ctx.new_list(vec![]);
            dict.set_item("__notes__", new_notes.clone().into(), vm)?;
            new_notes.into()
        };

        let notes = notes
            .downcast::<PyList>()
            .map_err(|_| vm.new_type_error("Cannot add note: __notes__ is not a list"))?;

        notes.borrow_vec_mut().push(note.into());
        Ok(())
    }

    #[pymethod]
    fn __reduce__(&self, vm: &VirtualMachine) -> PyTupleRef {
        if let Some(dict) = self.as_object().dict().filter(|x| !x.is_empty()) {
            vm.new_tuple((self.class().to_owned(), self.args(), dict))
        } else {
            vm.new_tuple((self.class().to_owned(), self.args()))
        }
    }

    #[pymethod]
    fn __setstate__(&self, state: PyObjectRef, vm: &VirtualMachine) -> PyResult<PyObjectRef> {
        if !vm.is_none(&state) {
            let dict = state
                .downcast::<crate::builtins::PyDict>()
                .map_err(|_| vm.new_type_error("state is not a dictionary"))?;

            for (key, value) in &dict {
                let key_str = key.str(vm)?;
                if key_str.as_bytes().starts_with(b"__") {
                    continue;
                }
                self.as_object().set_attr(&key_str, value, vm)?;
            }
        }
        Ok(vm.ctx.none())
    }

    #[pygetset]
    fn __dict__(zelf: PyObjectRef, vm: &VirtualMachine) -> PyResult<crate::builtins::PyDictRef> {
        crate::builtins::object::object_get_dict(zelf, vm)
    }

    #[pygetset(setter)]
    fn set___dict__(zelf: PyObjectRef, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
        crate::builtins::object::object_generic_set_dict(zelf, value, vm)
    }

    #[pygetset]
    pub fn args(&self) -> PyTupleRef {
        self.payload.args()
    }

    #[pygetset(setter)]
    fn set_args(&self, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
        let PySetterValue::Assign(value) = value else {
            return Err(vm.new_type_error("args may not be deleted"));
        };
        let args: ArgIterable = value.try_into_value(vm)?;
        let args = args.iter(vm)?.collect::<PyResult<Vec<_>>>()?;
        *self.args.write() = PyTuple::new_ref(args, &vm.ctx);
        Ok(())
    }

    #[pygetset]
    pub fn __traceback__(&self) -> Option<PyTracebackRef> {
        self.payload.__traceback__()
    }

    #[pygetset(setter)]
    fn set___traceback__(&self, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
        let PySetterValue::Assign(value) = value else {
            return Err(vm.new_type_error("__traceback__ may not be deleted"));
        };
        let traceback = if vm.is_none(&value) {
            None
        } else {
            match value.downcast::<PyTraceback>() {
                Ok(tb) => Some(tb),
                Err(_) => {
                    return Err(vm.new_type_error("__traceback__ must be a traceback or None"));
                }
            }
        };
        self.set_traceback(traceback);
        Ok(())
    }

    #[pygetset]
    pub fn __cause__(&self) -> Option<PyRef<PyBaseException>> {
        self.payload.__cause__()
    }

    #[pygetset(setter)]
    fn set___cause__(&self, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
        let PySetterValue::Assign(value) = value else {
            return Err(vm.new_type_error("__cause__ may not be deleted"));
        };
        let cause = if vm.is_none(&value) {
            None
        } else {
            match value.downcast::<PyBaseException>() {
                Ok(exc) => Some(exc),
                Err(_) => {
                    return Err(vm.new_type_error(
                        "exception cause must be None or derive from BaseException",
                    ));
                }
            }
        };
        self.set_cause(cause);
        Ok(())
    }

    #[pygetset]
    pub fn __context__(&self) -> Option<PyRef<PyBaseException>> {
        self.payload.__context__()
    }

    #[pygetset(setter)]
    fn set___context__(&self, value: PySetterValue, vm: &VirtualMachine) -> PyResult<()> {
        let PySetterValue::Assign(value) = value else {
            return Err(vm.new_type_error("__context__ may not be deleted"));
        };
        let context = if vm.is_none(&value) {
            None
        } else {
            match value.downcast::<PyBaseException>() {
                Ok(exc) => Some(exc),
                Err(_) => {
                    return Err(vm.new_type_error(
                        "exception context must be None or derive from BaseException",
                    ));
                }
            }
        };
        self.set_context(context);
        Ok(())
    }
}

#[pyclass]
impl PyRef<PyBaseException> {
    #[pymethod]
    fn with_traceback(self, tb: Option<PyTracebackRef>) -> Self {
        *self.traceback.write() = tb;
        self
    }
}

impl Constructor for PyBaseException {
    type Args = FuncArgs;

    fn slot_new(cls: PyTypeRef, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
        if cls.is(Self::class(&vm.ctx)) && !args.kwargs.is_empty() {
            return Err(vm.new_type_error("BaseException() takes no keyword arguments"));
        }
        Self::new(args.args, vm)
            .into_ref_with_type_lazy_dict(vm, cls)
            .map(Into::into)
    }

    fn py_new(_cls: &Py<PyType>, _args: FuncArgs, _vm: &VirtualMachine) -> PyResult<Self> {
        unimplemented!("use slot_new")
    }
}

impl Initializer for PyBaseException {
    type Args = FuncArgs;

    fn init(zelf: &Py<Self>, args: Self::Args, vm: &VirtualMachine) -> PyResult<()> {
        *zelf.args.write() = PyTuple::new_ref(args.args, &vm.ctx);
        Ok(())
    }
}

impl Representable for PyBaseException {
    #[inline]
    fn repr_str(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<String> {
        let repr_args = vm.exception_args_as_string(&zelf.args(), false);
        let cls = zelf.class();
        Ok(format!("{}({})", cls.name(), repr_args.iter().format(", ")))
    }
}

impl ExceptionZoo {
    pub(crate) fn init() -> Self {
        use self::types::*;

        let base_exception_type = PyBaseException::init_builtin_type();

        // Sorted By Hierarchy then alphabetized.
        let base_exception_group = PyBaseExceptionGroup::init_builtin_type();
        let system_exit = PySystemExit::init_builtin_type();
        let keyboard_interrupt = PyKeyboardInterrupt::init_builtin_type();
        let generator_exit = PyGeneratorExit::init_builtin_type();

        let exception_type = PyException::init_builtin_type();
        let stop_iteration = PyStopIteration::init_builtin_type();
        let stop_async_iteration = PyStopAsyncIteration::init_builtin_type();
        let arithmetic_error = PyArithmeticError::init_builtin_type();
        let floating_point_error = PyFloatingPointError::init_builtin_type();
        let overflow_error = PyOverflowError::init_builtin_type();
        let zero_division_error = PyZeroDivisionError::init_builtin_type();

        let assertion_error = PyAssertionError::init_builtin_type();
        let attribute_error = PyAttributeError::init_builtin_type();
        let buffer_error = PyBufferError::init_builtin_type();
        let eof_error = PyEOFError::init_builtin_type();

        let import_error = PyImportError::init_builtin_type();
        let module_not_found_error = PyModuleNotFoundError::init_builtin_type();

        let lookup_error = PyLookupError::init_builtin_type();
        let index_error = PyIndexError::init_builtin_type();
        let key_error = PyKeyError::init_builtin_type();

        let memory_error = PyMemoryError::init_builtin_type();

        let name_error = PyNameError::init_builtin_type();
        let unbound_local_error = PyUnboundLocalError::init_builtin_type();

        // os errors
        let os_error = PyOSError::init_builtin_type();
        let blocking_io_error = PyBlockingIOError::init_builtin_type();
        let child_process_error = PyChildProcessError::init_builtin_type();

        let connection_error = PyConnectionError::init_builtin_type();
        let broken_pipe_error = PyBrokenPipeError::init_builtin_type();
        let connection_aborted_error = PyConnectionAbortedError::init_builtin_type();
        let connection_refused_error = PyConnectionRefusedError::init_builtin_type();
        let connection_reset_error = PyConnectionResetError::init_builtin_type();

        let file_exists_error = PyFileExistsError::init_builtin_type();
        let file_not_found_error = PyFileNotFoundError::init_builtin_type();
        let interrupted_error = PyInterruptedError::init_builtin_type();
        let is_a_directory_error = PyIsADirectoryError::init_builtin_type();
        let not_a_directory_error = PyNotADirectoryError::init_builtin_type();
        let permission_error = PyPermissionError::init_builtin_type();
        let process_lookup_error = PyProcessLookupError::init_builtin_type();
        let timeout_error = PyTimeoutError::init_builtin_type();

        let reference_error = PyReferenceError::init_builtin_type();

        let runtime_error = PyRuntimeError::init_builtin_type();
        let not_implemented_error = PyNotImplementedError::init_builtin_type();
        let recursion_error = PyRecursionError::init_builtin_type();
        let python_finalization_error = PyPythonFinalizationError::init_builtin_type();

        let syntax_error = PySyntaxError::init_builtin_type();
        let incomplete_input_error = PyIncompleteInputError::init_builtin_type();
        let indentation_error = PyIndentationError::init_builtin_type();
        let tab_error = PyTabError::init_builtin_type();

        let system_error = PySystemError::init_builtin_type();
        let type_error = PyTypeError::init_builtin_type();
        let value_error = PyValueError::init_builtin_type();
        let unicode_error = PyUnicodeError::init_builtin_type();
        let unicode_decode_error = PyUnicodeDecodeError::init_builtin_type();
        let unicode_encode_error = PyUnicodeEncodeError::init_builtin_type();
        let unicode_translate_error = PyUnicodeTranslateError::init_builtin_type();

        #[cfg(feature = "jit")]
        let jit_error = PyJitError::init_builtin_type();

        let warning = PyWarning::init_builtin_type();
        let deprecation_warning = PyDeprecationWarning::init_builtin_type();
        let pending_deprecation_warning = PyPendingDeprecationWarning::init_builtin_type();
        let runtime_warning = PyRuntimeWarning::init_builtin_type();
        let syntax_warning = PySyntaxWarning::init_builtin_type();
        let user_warning = PyUserWarning::init_builtin_type();
        let future_warning = PyFutureWarning::init_builtin_type();
        let import_warning = PyImportWarning::init_builtin_type();
        let unicode_warning = PyUnicodeWarning::init_builtin_type();
        let bytes_warning = PyBytesWarning::init_builtin_type();
        let resource_warning = PyResourceWarning::init_builtin_type();
        let encoding_warning = PyEncodingWarning::init_builtin_type();

        Self {
            base_exception_type,
            base_exception_group,
            system_exit,
            keyboard_interrupt,
            generator_exit,
            exception_type,
            stop_iteration,
            stop_async_iteration,
            arithmetic_error,
            floating_point_error,
            overflow_error,
            zero_division_error,
            assertion_error,
            attribute_error,
            buffer_error,
            eof_error,
            import_error,
            module_not_found_error,
            lookup_error,
            index_error,
            key_error,
            memory_error,
            name_error,
            unbound_local_error,
            os_error,
            blocking_io_error,
            child_process_error,
            connection_error,
            broken_pipe_error,
            connection_aborted_error,
            connection_refused_error,
            connection_reset_error,
            file_exists_error,
            file_not_found_error,
            interrupted_error,
            is_a_directory_error,
            not_a_directory_error,
            permission_error,
            process_lookup_error,
            timeout_error,
            reference_error,
            runtime_error,
            not_implemented_error,
            recursion_error,
            python_finalization_error,
            syntax_error,
            incomplete_input_error,
            indentation_error,
            tab_error,
            system_error,
            type_error,
            value_error,
            unicode_error,
            unicode_decode_error,
            unicode_encode_error,
            unicode_translate_error,

            #[cfg(feature = "jit")]
            jit_error,

            warning,
            deprecation_warning,
            pending_deprecation_warning,
            runtime_warning,
            syntax_warning,
            user_warning,
            future_warning,
            import_warning,
            unicode_warning,
            bytes_warning,
            resource_warning,
            encoding_warning,
        }
    }

    // TODO: remove it after fixing `errno` / `winerror` problem
    #[allow(
        clippy::redundant_clone,
        reason = "temporary workaround until errno/winerror handling is fixed"
    )]
    pub fn extend(ctx: &'static Context) {
        use self::types::*;

        let excs = &ctx.exceptions;

        PyBaseException::extend_class(ctx, excs.base_exception_type);

        // Sorted By Hierarchy then alphabetized.
        extend_exception!(PyBaseExceptionGroup, ctx, excs.base_exception_group);

        extend_exception!(PySystemExit, ctx, excs.system_exit);
        extend_exception!(PyKeyboardInterrupt, ctx, excs.keyboard_interrupt);
        extend_exception!(PyGeneratorExit, ctx, excs.generator_exit);

        extend_exception!(PyException, ctx, excs.exception_type);

        extend_exception!(PyStopIteration, ctx, excs.stop_iteration);
        extend_exception!(PyStopAsyncIteration, ctx, excs.stop_async_iteration);

        extend_exception!(PyArithmeticError, ctx, excs.arithmetic_error);
        extend_exception!(PyFloatingPointError, ctx, excs.floating_point_error);
        extend_exception!(PyOverflowError, ctx, excs.overflow_error);
        extend_exception!(PyZeroDivisionError, ctx, excs.zero_division_error);

        extend_exception!(PyAssertionError, ctx, excs.assertion_error);
        extend_exception!(PyAttributeError, ctx, excs.attribute_error);
        extend_exception!(PyBufferError, ctx, excs.buffer_error);
        extend_exception!(PyEOFError, ctx, excs.eof_error);

        extend_exception!(PyImportError, ctx, excs.import_error);
        extend_exception!(PyModuleNotFoundError, ctx, excs.module_not_found_error);

        extend_exception!(PyLookupError, ctx, excs.lookup_error);
        extend_exception!(PyIndexError, ctx, excs.index_error);

        extend_exception!(PyKeyError, ctx, excs.key_error);

        extend_exception!(PyMemoryError, ctx, excs.memory_error);
        extend_exception!(PyNameError, ctx, excs.name_error);
        extend_exception!(PyUnboundLocalError, ctx, excs.unbound_local_error);

        // os errors:
        // PyOSError now uses struct fields with pygetset, no need for dynamic attributes
        extend_exception!(PyOSError, ctx, excs.os_error);

        extend_exception!(PyBlockingIOError, ctx, excs.blocking_io_error);
        extend_exception!(PyChildProcessError, ctx, excs.child_process_error);

        extend_exception!(PyConnectionError, ctx, excs.connection_error);
        extend_exception!(PyBrokenPipeError, ctx, excs.broken_pipe_error);
        extend_exception!(PyConnectionAbortedError, ctx, excs.connection_aborted_error);
        extend_exception!(PyConnectionRefusedError, ctx, excs.connection_refused_error);
        extend_exception!(PyConnectionResetError, ctx, excs.connection_reset_error);

        extend_exception!(PyFileExistsError, ctx, excs.file_exists_error);
        extend_exception!(PyFileNotFoundError, ctx, excs.file_not_found_error);
        extend_exception!(PyInterruptedError, ctx, excs.interrupted_error);
        extend_exception!(PyIsADirectoryError, ctx, excs.is_a_directory_error);
        extend_exception!(PyNotADirectoryError, ctx, excs.not_a_directory_error);
        extend_exception!(PyPermissionError, ctx, excs.permission_error);
        extend_exception!(PyProcessLookupError, ctx, excs.process_lookup_error);
        extend_exception!(PyTimeoutError, ctx, excs.timeout_error);

        extend_exception!(PyReferenceError, ctx, excs.reference_error);
        extend_exception!(PyRuntimeError, ctx, excs.runtime_error);
        extend_exception!(PyNotImplementedError, ctx, excs.not_implemented_error);
        extend_exception!(PyRecursionError, ctx, excs.recursion_error);
        extend_exception!(
            PyPythonFinalizationError,
            ctx,
            excs.python_finalization_error
        );

        extend_exception!(PySyntaxError, ctx, excs.syntax_error);
        extend_exception!(PyIncompleteInputError, ctx, excs.incomplete_input_error);
        extend_exception!(PyIndentationError, ctx, excs.indentation_error);
        extend_exception!(PyTabError, ctx, excs.tab_error);

        extend_exception!(PySystemError, ctx, excs.system_error);
        extend_exception!(PyTypeError, ctx, excs.type_error);
        extend_exception!(PyValueError, ctx, excs.value_error);
        extend_exception!(PyUnicodeError, ctx, excs.unicode_error);
        extend_exception!(PyUnicodeDecodeError, ctx, excs.unicode_decode_error);
        extend_exception!(PyUnicodeEncodeError, ctx, excs.unicode_encode_error);
        extend_exception!(PyUnicodeTranslateError, ctx, excs.unicode_translate_error);

        #[cfg(feature = "jit")]
        extend_exception!(PyJitError, ctx, excs.jit_error);

        extend_exception!(PyWarning, ctx, excs.warning);
        extend_exception!(PyDeprecationWarning, ctx, excs.deprecation_warning);
        extend_exception!(
            PyPendingDeprecationWarning,
            ctx,
            excs.pending_deprecation_warning
        );
        extend_exception!(PyRuntimeWarning, ctx, excs.runtime_warning);
        extend_exception!(PySyntaxWarning, ctx, excs.syntax_warning);
        extend_exception!(PyUserWarning, ctx, excs.user_warning);
        extend_exception!(PyFutureWarning, ctx, excs.future_warning);
        extend_exception!(PyImportWarning, ctx, excs.import_warning);
        extend_exception!(PyUnicodeWarning, ctx, excs.unicode_warning);
        extend_exception!(PyBytesWarning, ctx, excs.bytes_warning);
        extend_exception!(PyResourceWarning, ctx, excs.resource_warning);
        extend_exception!(PyEncodingWarning, ctx, excs.encoding_warning);
    }
}

#[cfg(feature = "serde")]
pub struct SerializeException<'vm, 's> {
    vm: &'vm VirtualMachine,
    exc: &'s Py<PyBaseException>,
}

#[cfg(feature = "serde")]
impl<'vm, 's> SerializeException<'vm, 's> {
    pub fn new(vm: &'vm VirtualMachine, exc: &'s Py<PyBaseException>) -> Self {
        SerializeException { vm, exc }
    }
}

#[cfg(feature = "serde")]
pub struct SerializeExceptionOwned<'vm> {
    vm: &'vm VirtualMachine,
    exc: PyBaseExceptionRef,
}

#[cfg(feature = "serde")]
impl serde::Serialize for SerializeExceptionOwned<'_> {
    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        let Self { vm, exc } = self;
        SerializeException::new(vm, exc).serialize(s)
    }
}

#[cfg(feature = "serde")]
impl serde::Serialize for SerializeException<'_, '_> {
    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        use serde::ser::*;

        let mut struc = s.serialize_struct("PyBaseException", 7)?;
        struc.serialize_field("exc_type", &*self.exc.class().name())?;
        let tbs = {
            struct Tracebacks(PyTracebackRef);
            impl serde::Serialize for Tracebacks {
                fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
                    let mut s = s.serialize_seq(None)?;
                    for tb in self.0.iter() {
                        s.serialize_element(&**tb)?;
                    }
                    s.end()
                }
            }
            self.exc.traceback().map(Tracebacks)
        };
        struc.serialize_field("traceback", &tbs)?;
        struc.serialize_field(
            "cause",
            &self
                .exc
                .__cause__()
                .map(|exc| SerializeExceptionOwned { vm: self.vm, exc }),
        )?;
        struc.serialize_field(
            "context",
            &self
                .exc
                .__context__()
                .map(|exc| SerializeExceptionOwned { vm: self.vm, exc }),
        )?;
        struc.serialize_field("suppress_context", &self.exc.__suppress_context__())?;

        let args = {
            struct Args<'vm>(&'vm VirtualMachine, PyTupleRef);
            impl serde::Serialize for Args<'_> {
                fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
                    s.collect_seq(
                        self.1
                            .as_slice()
                            .iter()
                            .map(|arg| crate::py_serde::PyObjectSerializer::new(self.0, arg)),
                    )
                }
            }
            Args(self.vm, self.exc.args())
        };
        struc.serialize_field("args", &args)?;

        let rendered = {
            let mut rendered = String::new();
            self.vm
                .write_exception(&mut rendered, self.exc)
                .map_err(S::Error::custom)?;
            rendered
        };
        struc.serialize_field("rendered", &rendered)?;

        struc.end()
    }
}

#[derive(Debug)]
pub struct NulError;

impl Display for NulError {
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        write!(f, "embedded null character")
    }
}

pub fn nul_char_error(vm: &VirtualMachine) -> PyBaseExceptionRef {
    vm.new_value_error("embedded null character")
}

pub fn nul_char_type_error(vm: &VirtualMachine) -> PyBaseExceptionRef {
    vm.new_type_error("embedded null character")
}

pub fn nul_byte_error(vm: &VirtualMachine) -> PyBaseExceptionRef {
    vm.new_value_error("embedded null byte")
}

impl ToPyException for alloc::ffi::NulError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

impl ToPyException for alloc::ffi::FromVecWithNulError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

impl ToPyException for core::ffi::FromBytesWithNulError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

impl ToPyException for NulError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

#[cfg(windows)]
impl<C> ToPyException for widestring::error::ContainsNul<C> {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

#[cfg(windows)]
impl ToPyException for widestring::error::MissingNulTerminator {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

#[cfg(windows)]
impl<C> ToPyException for widestring::error::NulError<C> {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        nul_char_error(vm)
    }
}

#[cfg(any(unix, windows, target_os = "wasi"))]
pub(crate) fn errno_to_exc_type(errno: i32, vm: &VirtualMachine) -> Option<&'static Py<PyType>> {
    use crate::stdlib::errno::errors;
    let excs = &vm.ctx.exceptions;
    match errno {
        #[allow(unreachable_patterns)] // EAGAIN is sometimes the same as EWOULDBLOCK
        errors::EWOULDBLOCK | errors::EAGAIN => Some(excs.blocking_io_error),
        errors::EALREADY => Some(excs.blocking_io_error),
        errors::EINPROGRESS => Some(excs.blocking_io_error),
        errors::EPIPE => Some(excs.broken_pipe_error),
        #[cfg(not(target_os = "wasi"))]
        errors::ESHUTDOWN => Some(excs.broken_pipe_error),
        errors::ECHILD => Some(excs.child_process_error),
        errors::ECONNABORTED => Some(excs.connection_aborted_error),
        errors::ECONNREFUSED => Some(excs.connection_refused_error),
        errors::ECONNRESET => Some(excs.connection_reset_error),
        errors::EEXIST => Some(excs.file_exists_error),
        errors::ENOENT => Some(excs.file_not_found_error),
        errors::EISDIR => Some(excs.is_a_directory_error),
        errors::ENOTDIR => Some(excs.not_a_directory_error),
        errors::EINTR => Some(excs.interrupted_error),
        errors::EACCES => Some(excs.permission_error),
        errors::EPERM => Some(excs.permission_error),
        // A process without the capability to reach a resource.
        #[cfg(target_vendor = "apple")]
        errors::ENOTCAPABLE => Some(excs.permission_error),
        errors::ESRCH => Some(excs.process_lookup_error),
        errors::ETIMEDOUT => Some(excs.timeout_error),
        _ => None,
    }
}

#[cfg(all(target_arch = "wasm32", not(target_os = "wasi")))]
pub(crate) fn errno_to_exc_type(_errno: i32, _vm: &VirtualMachine) -> Option<&'static Py<PyType>> {
    None
}

pub(crate) trait ToOSErrorBuilder {
    fn to_os_error_builder(&self, vm: &VirtualMachine) -> OSErrorBuilder;
}

pub(crate) struct OSErrorBuilder {
    exc_type: PyTypeRef,
    errno: Option<i32>,
    strerror: Option<PyObjectRef>,
    filename: Option<PyObjectRef>,
    #[cfg(windows)]
    winerror: Option<PyObjectRef>,
    filename2: Option<PyObjectRef>,
}

impl OSErrorBuilder {
    #[must_use]
    pub(crate) fn with_subtype(
        exc_type: PyTypeRef,
        errno: Option<i32>,
        strerror: impl ToPyObject,
        vm: &VirtualMachine,
    ) -> Self {
        let strerror = strerror.to_pyobject(vm);
        Self {
            exc_type,
            errno,
            strerror: Some(strerror),
            filename: None,
            #[cfg(windows)]
            winerror: None,
            filename2: None,
        }
    }

    #[must_use]
    pub(crate) fn with_errno(errno: i32, strerror: impl ToPyObject, vm: &VirtualMachine) -> Self {
        let exc_type = errno_to_exc_type(errno, vm)
            .unwrap_or(vm.ctx.exceptions.os_error)
            .to_owned();
        Self::with_subtype(exc_type, Some(errno), strerror, vm)
    }

    #[must_use]
    #[allow(dead_code)]
    pub(crate) fn filename(mut self, filename: PyObjectRef) -> Self {
        self.filename.replace(filename);
        self
    }

    #[must_use]
    #[allow(dead_code)]
    pub(crate) fn filename2(mut self, filename: PyObjectRef) -> Self {
        self.filename2.replace(filename);
        self
    }

    #[must_use]
    #[cfg(windows)]
    pub(crate) fn winerror(mut self, winerror: PyObjectRef) -> Self {
        self.winerror.replace(winerror);
        self
    }

    /// Strip winerror from the builder. Used for C runtime errors
    /// (e.g. `_wopen`, `open`) that should produce `[Errno X]` format
    /// instead of `[WinError X]`.
    #[must_use]
    #[cfg(windows)]
    pub(crate) fn without_winerror(mut self) -> Self {
        self.winerror = None;
        self
    }

    pub(crate) fn build(self, vm: &VirtualMachine) -> PyRef<types::PyOSError> {
        use types::PyOSError;

        let Self {
            exc_type,
            errno,
            strerror,
            filename,
            #[cfg(windows)]
            winerror,
            filename2,
        } = self;

        let args = if let Some(errno) = errno {
            let winerror = cfg_select! {
                windows => winerror.to_pyobject(vm),
                _ => vm.ctx.none(),
            };

            vec![
                errno.to_pyobject(vm),
                strerror.to_pyobject(vm),
                filename.to_pyobject(vm),
                winerror,
                filename2.to_pyobject(vm),
            ]
        } else {
            vec![strerror.to_pyobject(vm)]
        };

        vm.new_payload_exception::<PyOSError>(exc_type, args.into())
            .expect("new_os_error usage error")
    }
}

impl IntoPyException for OSErrorBuilder {
    fn into_pyexception(self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        self.build(vm).upcast()
    }
}

impl ToOSErrorBuilder for std::io::Error {
    fn to_os_error_builder(&self, vm: &VirtualMachine) -> OSErrorBuilder {
        use crate::host_env::os::ErrorExt;

        let errno = self.posix_errno();
        #[cfg(windows)]
        let msg = 'msg: {
            // Use C runtime's strerror for POSIX errno values.
            // For Windows-specific error codes, fall back to FormatMessage.
            const MAX_POSIX_ERRNO: i32 = 127;
            if errno > 0
                && errno <= MAX_POSIX_ERRNO
                && let Some(s) = crate::host_env::errno::strerror_string(errno)
                && !s.starts_with("Unknown error")
            {
                break 'msg s;
            }
            self.to_string()
        };
        #[cfg(unix)]
        let msg =
            crate::host_env::errno::strerror_string(errno).unwrap_or_else(|| self.to_string());
        #[cfg(not(any(windows, unix)))]
        let msg = self.to_string();

        #[allow(unused_mut)]
        let mut builder = OSErrorBuilder::with_errno(errno, msg, vm);
        #[cfg(windows)]
        if let Some(winerror) = self.raw_os_error() {
            builder = builder.winerror(winerror.to_pyobject(vm));
        }
        builder
    }
}

impl ToPyException for std::io::Error {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        let builder = self.to_os_error_builder(vm);
        builder.into_pyexception(vm)
    }
}

impl IntoPyException for std::io::Error {
    fn into_pyexception(self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        self.to_pyexception(vm)
    }
}

#[cfg(all(unix, not(target_os = "redox")))]
impl ToPyException for rustpython_host_env::fcntl::LockfError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::InvalidCmd => vm.new_value_error("unrecognized lockf argument"),
            Self::Overflow(e) => vm.new_overflow_error(e.clone()),
            Self::Io(err) => err.to_pyexception(vm),
        }
    }
}

#[cfg(unix)]
impl ToPyException for rustpython_host_env::posix::AccessError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::InvalidMode => vm.new_value_error(
                "One of the flags is wrong, there are only 4 possibilities F_OK, R_OK, W_OK and X_OK",
            ),
            Self::Os(errno) => std::io::Error::from_raw_os_error(*errno).to_pyexception(vm),
        }
    }
}

#[cfg(all(unix, not(target_os = "redox")))]
impl ToPyException for rustpython_host_env::socket::AncillaryPackError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::ItemTooLarge => vm.new_os_error("ancillary data item too large"),
            Self::TooMuchData => vm.new_os_error("too much ancillary data"),
            Self::UnexpectedNullHeader => {
                vm.new_runtime_error("unexpected NULL result from CMSG_FIRSTHDR/CMSG_NXTHDR")
            }
        }
    }
}

#[cfg(any(unix, windows))]
impl ToPyException for rustpython_host_env::time::CheckedTmError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::YearOutOfRange => vm.new_overflow_error("year out of range"),
            Self::MonthOutOfRange => vm.new_value_error("month out of range"),
            Self::DayOfMonthOutOfRange => vm.new_value_error("day of month out of range"),
            Self::HourOutOfRange => vm.new_value_error("hour out of range"),
            Self::MinuteOutOfRange => vm.new_value_error("minute out of range"),
            Self::SecondsOutOfRange => vm.new_value_error("seconds out of range"),
            Self::DayOfWeekOutOfRange => vm.new_value_error("day of week out of range"),
            Self::DayOfYearOutOfRange => vm.new_value_error("day of year out of range"),
            Self::EmbeddedNul => vm.new_value_error("embedded null character"),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::winapi::BuildEnvironmentBlockError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::ContainsNul => vm.new_value_error("embedded null character"),
            Self::IllegalName => vm.new_value_error("illegal environment variable name"),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::winapi::BatchedWaitError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::Timeout => vm
                .new_os_subtype_error(
                    vm.ctx.exceptions.timeout_error.to_owned(),
                    None,
                    "timed out",
                )
                .upcast(),
            Self::Interrupted => vm
                .new_errno_error(libc::EINTR, "Interrupted system call")
                .upcast(),
            Self::Os(err) => vm.new_os_error(*err as i32),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::nt::ReadlinkError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::Io(err) => err.to_pyexception(vm),
            Self::NotSymbolicLink => {
                vm.new_os_error("The file or directory is not a reparse point")
            }
            Self::InvalidReparseData => vm.new_os_error("Invalid reparse data"),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::nt::ReadConsoleError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::Io(err) => err.to_pyexception(vm),
            Self::BufferTooSmall {
                available,
                required,
            } => vm.new_system_error(format!(
                "Buffer had room for {available} bytes but {required} bytes required",
            )),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::winreg::ExpandEnvironmentStringsError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::Os => vm.new_os_error("ExpandEnvironmentStringsW failed"),
            Self::Utf16(e) => vm.new_value_error(format!("UTF16 error: {e}")),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::winreg::QueryStringError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::Code(err) => std::io::Error::from_raw_os_error(*err as i32).to_pyexception(vm),
            Self::Utf16(e) => vm.new_value_error(format!("UTF16 error: {e}")),
        }
    }
}

#[cfg(windows)]
impl ToPyException for rustpython_host_env::wmi::ExecQueryError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        match self {
            Self::MoreData => vm.new_os_error(format!(
                "Query returns more than {} characters",
                rustpython_host_env::wmi::BUFFER_SIZE
            )),
            Self::Code(err) => std::io::Error::from_raw_os_error(*err as i32).to_pyexception(vm),
        }
    }
}

#[cfg(unix)]
impl ToPyException for rustpython_host_env::multiprocessing::SemError {
    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
        let excs = &vm.ctx.exceptions;
        let exc_type = match self {
            Self::AlreadyExists => excs.file_exists_error.to_owned(),
            Self::NotFound => excs.file_not_found_error.to_owned(),
            _ => excs.os_error.to_owned(),
        };
        vm.new_os_subtype_error(exc_type, Some(self.raw_os_error()), self.description())
            .upcast()
    }
}

pub(super) mod types {
    use crate::class::PyClassDef;
    use crate::common::lock::PyRwLock;
    use crate::object::{Traverse, TraverseFn};
    #[cfg_attr(target_arch = "wasm32", allow(unused_imports))]
    use crate::{
        AsObject, Py, PyAtomicRef, PyObject, PyObjectRef, PyPayload, PyRef, PyResult,
        VirtualMachine,
        builtins::{
            PyInt, PyStrRef, PyTupleRef, PyType, PyTypeRef, traceback::PyTracebackRef,
            tuple::IntoPyTuple,
        },
        convert::ToPyResult,
        function::{ArgBytesLike, FuncArgs, KwArgs, PySetterValue},
        types::{Constructor, Initializer},
    };
    use core::sync::atomic::{AtomicBool, AtomicIsize, Ordering};
    use crossbeam_utils::atomic::AtomicCell;
    use itertools::Itertools;
    use rustpython_common::{
        str::UnicodeEscapeCodepoint,
        wtf8::{Wtf8, Wtf8Buf, wtf8_concat},
    };

    // Re-export exception group types from dedicated module
    pub use crate::exception_group::types::PyBaseExceptionGroup;

    // This module is designed to be used as `use builtins::*;`.
    // Do not add any pub symbols not included in builtins module.
    // `PyBaseExceptionRef` is the only exception.

    pub type PyBaseExceptionRef = PyRef<PyBaseException>;

    // Sorted By Hierarchy then alphabetized.

    #[pyclass(module = false, name = "BaseException", traverse = "manual")]
    pub struct PyBaseException {
        pub(super) traceback: PyRwLock<Option<PyTracebackRef>>,
        pub(super) cause: PyRwLock<Option<PyRef<Self>>>,
        pub(super) context: PyRwLock<Option<PyRef<Self>>>,
        #[pymember(name = "__suppress_context__", writable)]
        pub(super) suppress_context: AtomicBool,
        pub(super) args: PyRwLock<PyTupleRef>,
    }

    #[pyexception(name, base = PyBaseException, ctx = "system_exit", traverse = "manual")]
    #[repr(C)]
    pub struct PySystemExit {
        base: PyBaseException,
        #[pymember(writable)]
        code: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PySystemExit {
        type Base = PyBaseException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    unsafe impl Traverse for PySystemExit {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.traverse(tracer_fn);
            if let Some(obj) = self.code.deref() {
                tracer_fn(obj);
            }
        }
    }

    impl core::fmt::Debug for PySystemExit {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PySystemExit").finish_non_exhaustive()
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PySystemExit {}

    impl Initializer for PySystemExit {
        type Args = FuncArgs;
        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            // Call BaseException_init first (handles args)
            let code = match args.args.len() {
                0 => vm.ctx.none(),
                1 => args.args[0].clone(),
                _ => vm.ctx.new_tuple(args.args.clone()).into(),
            };
            PyBaseException::slot_init(zelf, args, vm)?;
            let exc: &Py<Self> = zelf.downcast_ref::<Self>().unwrap();
            exc.code.swap_to_temporary_refs(Some(code), vm);
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    impl Constructor for PySystemExit {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            let base_exception = PyBaseException::new(args.args, vm);
            Ok(Self {
                base: base_exception,
                code: None.into(),
            })
        }
    }

    #[pyexception(name, base = PyBaseException, ctx = "generator_exit", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyGeneratorExit(PyBaseException);

    #[pyexception(name, base = PyBaseException, ctx = "keyboard_interrupt", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyKeyboardInterrupt(PyBaseException);

    #[pyexception(name, base = PyBaseException, ctx = "exception_type", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyException(PyBaseException);

    #[pyexception(name, base = PyException, ctx = "stop_iteration", traverse = "manual")]
    #[repr(C)]
    pub struct PyStopIteration {
        base: PyException,
        #[pymember(writable)]
        value: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PyStopIteration {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyStopIteration {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyStopIteration").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyStopIteration {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.traverse(tracer_fn);
            if let Some(obj) = self.value.deref() {
                tracer_fn(obj);
            }
        }
    }

    impl Constructor for PyStopIteration {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            let base_exception = PyBaseException::new(args.args, vm);
            Ok(Self {
                base: PyException(base_exception),
                value: None.into(),
            })
        }
    }

    impl Initializer for PyStopIteration {
        type Args = FuncArgs;
        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            let value = match args.args.len() {
                0 => vm.ctx.none(),
                _ => args.args[0].clone(),
            };
            PyBaseException::slot_init(zelf, args, vm)?;
            let exc: &Py<Self> = zelf.downcast_ref::<Self>().unwrap();
            exc.value.swap_to_temporary_refs(Some(value), vm);
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PyStopIteration {}

    #[pyexception(name, base = PyException, ctx = "stop_async_iteration", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyStopAsyncIteration(PyException);

    #[pyexception(name, base = PyException, ctx = "arithmetic_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyArithmeticError(PyException);

    #[pyexception(name, base = PyArithmeticError, ctx = "floating_point_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyFloatingPointError(PyArithmeticError);

    #[pyexception(name, base = PyArithmeticError, ctx = "overflow_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyOverflowError(PyArithmeticError);

    #[pyexception(name, base = PyArithmeticError, ctx = "zero_division_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyZeroDivisionError(PyArithmeticError);

    #[pyexception(name, base = PyException, ctx = "assertion_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyAssertionError(PyException);

    #[pyexception(name, base = PyException, ctx = "attribute_error", traverse = "manual")]
    #[repr(C)]
    pub struct PyAttributeError {
        base: PyException,
        #[pymember(writable)]
        name: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        obj: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PyAttributeError {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyAttributeError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyAttributeError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyAttributeError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.traverse(tracer_fn);
            if let Some(obj) = self.name.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.obj.deref() {
                tracer_fn(obj);
            }
        }
    }

    impl Constructor for PyAttributeError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            Ok(Self {
                base: PyException(PyBaseException::new(args.args, vm)),
                name: None.into(),
                obj: None.into(),
            })
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PyAttributeError {
        #[pymethod]
        fn __getstate__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult {
            let obj = zelf.as_object();
            let state = match obj.dict() {
                Some(dict) => dict.copy().into_ref(&vm.ctx),
                None => vm.ctx.new_dict(),
            };
            let _ = state.del_item("obj", vm);
            if let Some(name) = zelf.name.load_owned() {
                state.set_item("name", name, vm)?;
            }
            Ok(state.into())
        }

        #[pymethod]
        fn __reduce__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyTupleRef> {
            let state = Self::__getstate__(zelf, vm)?;
            let base: &Py<PyBaseException> = zelf
                .as_object()
                .downcast_ref()
                .expect("AttributeError is a BaseException");
            Ok(vm.ctx.new_tuple(vec![
                zelf.class().to_owned().into(),
                base.args().into(),
                state,
            ]))
        }
    }

    impl Initializer for PyAttributeError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            // Only 'name' and 'obj' kwargs are allowed
            let mut kwargs = args.kwargs.clone();
            let name = kwargs.swap_remove("name");
            let obj = kwargs.swap_remove("obj");

            // Reject unknown kwargs
            if let Some(invalid_key) = kwargs.keys().next() {
                return Err(vm.new_unexpected_keyword_type_error(
                    Some(Self::NAME),
                    &invalid_key.to_string(),
                ));
            }

            // Pass args without kwargs to BaseException_init
            let base_args = FuncArgs::new(args.args, KwArgs::default());
            PyBaseException::slot_init(zelf, base_args, vm)?;

            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("AttributeError instance has AttributeError payload");
            exc.name.swap_to_temporary_refs(name, vm);
            exc.obj.swap_to_temporary_refs(obj, vm);
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(name, base = PyException, ctx = "buffer_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyBufferError(PyException);

    #[pyexception(name, base = PyException, ctx = "eof_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyEOFError(PyException);

    #[pyexception(name, base = PyException, ctx = "import_error", traverse = "manual")]
    #[repr(C)]
    pub struct PyImportError {
        base: PyException,
        #[pymember(writable)]
        msg: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        name: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        path: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        name_from: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PyImportError {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyImportError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyImportError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyImportError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.traverse(tracer_fn);
            if let Some(obj) = self.msg.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.name.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.path.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.name_from.deref() {
                tracer_fn(obj);
            }
        }
    }

    impl Constructor for PyImportError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            Ok(Self {
                base: PyException(PyBaseException::new(args.args, vm)),
                msg: None.into(),
                name: None.into(),
                path: None.into(),
                name_from: None.into(),
            })
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PyImportError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("slot wrapper checked ImportError");
            if let Some(msg) = exc.msg.load_owned()
                && msg.class().is(vm.ctx.types.str_type)
            {
                return msg.str(vm);
            }
            let base: &Py<PyBaseException> =
                zelf.downcast_ref().expect("ImportError is a BaseException");
            Ok(base.__str__(vm))
        }

        #[pymethod]
        fn __reduce__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<PyTupleRef> {
            let obj = zelf.as_object();
            let exc = zelf;
            let base: &Py<PyBaseException> =
                obj.downcast_ref().expect("ImportError is a BaseException");
            let args: PyObjectRef = match base.get_arg(0) {
                Some(arg) => vm.new_tuple((arg,)).into(),
                None => base.args().into(),
            };
            let mut result: Vec<PyObjectRef> = vec![obj.class().to_owned().into(), args];

            let mut state = obj
                .dict()
                .filter(|dict| !dict.is_empty())
                .map(|dict| dict.copy().into_ref(&vm.ctx));
            let mut insert = |key: &str, value: Option<PyObjectRef>| -> PyResult<()> {
                let Some(value) = value else {
                    return Ok(());
                };
                let dict = state.get_or_insert_with(|| vm.ctx.new_dict());
                dict.set_item(key, value, vm)?;
                Ok(())
            };
            insert("name", exc.name.load_owned())?;
            insert("path", exc.path.load_owned())?;
            insert("name_from", exc.name_from.load_owned())?;
            if let Some(state) = state {
                result.push(state.into());
            }
            Ok(result.into_pytuple(vm))
        }
    }

    impl Initializer for PyImportError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            // Only 'name', 'path', 'name_from' kwargs are allowed
            let mut kwargs = args.kwargs.clone();
            let name = kwargs.swap_remove("name");
            let path = kwargs.swap_remove("path");
            let name_from = kwargs.swap_remove("name_from");

            // Check for any remaining invalid keyword arguments
            if let Some(invalid_key) = kwargs.keys().next() {
                return Err(vm.new_unexpected_keyword_type_error(
                    Some("ImportError"),
                    &invalid_key.to_string(),
                ));
            }

            let msg = if args.args.len() == 1 {
                Some(args.args[0].clone())
            } else {
                None
            };
            let base_args = FuncArgs::new(args.args, KwArgs::default());
            PyBaseException::slot_init(zelf, base_args, vm)?;
            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("ImportError instance has ImportError payload");
            exc.name.swap_to_temporary_refs(name, vm);
            exc.path.swap_to_temporary_refs(path, vm);
            exc.name_from.swap_to_temporary_refs(name_from, vm);
            exc.msg.swap_to_temporary_refs(msg, vm);
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(name, base = PyImportError, ctx = "module_not_found_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyModuleNotFoundError(PyImportError);

    #[pyexception(name, base = PyException, ctx = "lookup_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyLookupError(PyException);

    #[pyexception(name, base = PyLookupError, ctx = "index_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyIndexError(PyLookupError);

    #[pyexception(name, base = PyLookupError, ctx = "key_error")]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyKeyError(PyLookupError);

    #[pyexception]
    impl PyKeyError {
        #[pymethod]
        fn __str__(zelf: &Py<PyBaseException>, vm: &VirtualMachine) -> PyStrRef {
            let args = zelf.args();
            if args.as_slice().len() == 1 {
                vm.exception_args_as_string(&args, false)
                    .into_iter()
                    .exactly_one()
                    .unwrap()
            } else {
                zelf.__str__(vm)
            }
        }
    }

    #[pyexception(name, base = PyException, ctx = "memory_error", impl, payload = "manual", traverse = "manual")]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyMemoryError(PyException);

    impl PyMemoryError {
        pub(crate) fn empty(vm: &VirtualMachine) -> Self {
            Self(PyException(PyBaseException::new(vec![], vm)))
        }
    }

    unsafe impl Traverse for PyMemoryError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.0.0.traverse(tracer_fn);
        }

        fn clear(&mut self, out: &mut Vec<PyObjectRef>) {
            let base = &mut self.0.0;
            if let Some(traceback) = base.traceback.get_mut().take() {
                out.push(traceback.into());
            }

            if let Some(cause) = base.cause.get_mut().take() {
                out.push(cause.into());
            }

            if let Some(context) = base.context.get_mut().take() {
                out.push(context.into());
            }
        }
    }

    #[pyexception(name, base = PyException, ctx = "name_error", traverse = "manual")]
    #[repr(C)]
    pub struct PyNameError {
        base: PyException,
        #[pymember(writable)]
        name: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PyNameError {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyNameError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyNameError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyNameError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.traverse(tracer_fn);
            if let Some(obj) = self.name.deref() {
                tracer_fn(obj);
            }
        }
    }

    impl Constructor for PyNameError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            Ok(Self {
                base: PyException(PyBaseException::new(args.args, vm)),
                name: None.into(),
            })
        }
    }

    // NameError_init: handles the .name kwarg
    #[pyexception(with(Constructor, Initializer))]
    impl PyNameError {}

    impl Initializer for PyNameError {
        type Args = FuncArgs;
        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            // Only 'name' kwarg is allowed
            let mut kwargs = args.kwargs.clone();
            let name = kwargs.swap_remove("name");

            // Reject unknown kwargs
            if let Some(invalid_key) = kwargs.keys().next() {
                return Err(vm.new_unexpected_keyword_type_error(
                    Some(Self::NAME),
                    &invalid_key.to_string(),
                ));
            }

            // Pass args without kwargs to BaseException_init
            let base_args = FuncArgs::new(args.args, KwArgs::default());
            PyBaseException::slot_init(zelf, base_args, vm)?;

            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("NameError instance has NameError payload");
            // Absent keyword clears the field. Re-init must not keep the old name.
            exc.name.swap_to_temporary_refs(name, vm);
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(name, base = PyNameError, ctx = "unbound_local_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUnboundLocalError(PyNameError);

    #[pyexception(name, base = PyException, ctx = "os_error", traverse = "manual")]
    #[repr(C)]
    pub struct PyOSError {
        base: PyException,
        #[pymember(writable)]
        errno: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        strerror: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        filename: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        filename2: PyAtomicRef<Option<PyObject>>,
        #[cfg(windows)]
        #[pymember(writable)]
        winerror: PyAtomicRef<Option<PyObject>>,
        // For BlockingIOError: characters written before blocking occurred
        // -1 means not set (AttributeError when accessed)
        written: AtomicCell<isize>,
    }

    impl crate::class::PySubclass for PyOSError {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyOSError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyOSError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyOSError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            // `self.base` is a `PyException` newtype whose `MaybeTraverse` is a
            // no-op; reach the underlying `PyBaseException` so its traceback,
            // cause, context and args are visited by the collector.
            self.base.0.traverse(tracer_fn);
            if let Some(obj) = self.errno.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.strerror.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.filename.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.filename2.deref() {
                tracer_fn(obj);
            }
            #[cfg(windows)]
            if let Some(obj) = self.winerror.deref() {
                tracer_fn(obj);
            }
        }
    }

    // OS Errors:
    impl Constructor for PyOSError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            let len = args.args.len();
            // CPython only sets errno/strerror when args len is 2-5
            let (errno, strerror) = if (2..=5).contains(&len) {
                (Some(args.args[0].clone()), Some(args.args[1].clone()))
            } else {
                (None, None)
            };
            let filename = if (3..=5).contains(&len) {
                Some(args.args[2].clone())
            } else {
                None
            };
            let filename2 = if len == 5 {
                args.args.get(4).cloned()
            } else {
                None
            };
            // Truncate args for base exception when 3-5 args
            let base_args = if (3..=5).contains(&len) {
                args.args[..2].to_vec()
            } else {
                args.args.to_vec()
            };
            let base_exception = PyBaseException::new(base_args, vm);
            Ok(Self {
                base: PyException(base_exception),
                errno: errno.into(),
                strerror: strerror.into(),
                filename: filename.into(),
                filename2: filename2.into(),
                #[cfg(windows)]
                winerror: None.into(),
                written: AtomicCell::new(-1),
            })
        }

        fn slot_new(cls: PyTypeRef, args: FuncArgs, vm: &VirtualMachine) -> PyResult {
            if oserror_use_init(&cls) {
                let payload = Self {
                    base: PyException(PyBaseException::new(vec![], vm)),
                    errno: None.into(),
                    strerror: None.into(),
                    filename: None.into(),
                    filename2: None.into(),
                    #[cfg(windows)]
                    winerror: None.into(),
                    written: AtomicCell::new(-1),
                };
                return payload
                    .into_ref_with_type_lazy_dict(vm, cls)
                    .map(Into::into);
            }

            if !args.kwargs.is_empty() {
                return Err(
                    vm.new_type_error(format!("{}() takes no keyword arguments", cls.slot_name()))
                );
            }

            // We need this method, because of how `CPython` copies `init`
            // from `BaseException` in `SimpleExtendsException` macro.
            // See: `BaseException_new`
            if *cls.name() == *vm.ctx.exceptions.os_error.name() {
                let args_vec = args.args.to_vec();
                let len = args_vec.len();
                if (2..=5).contains(&len) {
                    let errno = &args_vec[0];
                    if let Some(error) = errno
                        .downcast_ref::<PyInt>()
                        .and_then(|errno| errno.try_to_primitive::<i32>(vm).ok())
                        .and_then(|errno| super::errno_to_exc_type(errno, vm))
                        .and_then(|typ| {
                            vm.new_payload_exception::<Self>(typ.to_owned(), args_vec.into())
                                .ok()
                        })
                    {
                        return error.to_pyresult(vm);
                    }
                }
            }
            let payload = Self::py_new(&cls, args.clone(), vm)?;
            let obj = payload.into_ref_with_type_lazy_dict(vm, cls)?;
            oserror_init(obj.as_object(), args, vm)?;
            Ok(obj.into())
        }
    }

    fn oserror_use_init(cls: &Py<PyType>) -> bool {
        let init = cls.slots.init.load();
        let new = cls.slots.new.load();
        let slot_init: fn(&PyObject, FuncArgs, &VirtualMachine) -> PyResult<()> =
            PyOSError::slot_init;
        let slot_new: fn(PyTypeRef, FuncArgs, &VirtualMachine) -> PyResult = PyOSError::slot_new;
        !matches!(init, Some(f) if core::ptr::fn_addr_eq(f, slot_init))
            && matches!(new, Some(f) if core::ptr::fn_addr_eq(f, slot_new))
    }

    fn oserror_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
        let len = args.args.len();
        let mut new_args = args;

        // All OSError subclasses use #[repr(transparent)] wrapping PyOSError,
        // so we can safely access the PyOSError fields through pointer cast
        // SAFETY: All OSError subclasses (FileNotFoundError, etc.) are
        // #[repr(transparent)] wrappers around PyOSError with identical memory layout
        #[allow(deprecated)]
        let exc: &Py<PyOSError> = zelf.downcast_ref::<PyOSError>().unwrap();

        // Check if this is BlockingIOError - need to handle characters_written
        let is_blocking_io_error = zelf
            .class()
            .is(vm.ctx.exceptions.blocking_io_error.as_ref());

        // SAFETY: slot_init is called during object initialization,
        // so fields are None and swap result can be safely ignored
        let mut set_filename = true;
        if len <= 5 {
            // Only set errno/strerror when args len is 2-5
            if 2 <= len {
                let _ = unsafe { exc.errno.swap(Some(new_args.args[0].clone())) };
                let _ = unsafe { exc.strerror.swap(Some(new_args.args[1].clone())) };
            }
            if 3 <= len {
                let third_arg = &new_args.args[2];
                // BlockingIOError's 3rd argument can be the number of characters written
                if is_blocking_io_error
                    && !vm.is_none(third_arg)
                    && crate::protocol::PyNumber::check(third_arg)
                    && let Ok(written) = third_arg.try_index(vm)
                    && let Ok(n) = written.try_to_primitive::<isize>(vm)
                {
                    exc.written.store(n);
                    set_filename = false;
                    // The count leaves neither filename taken, so both are
                    // put back the way `py_new` found them.
                    let _ = unsafe { exc.filename.swap(None) };
                    let _ = unsafe { exc.filename2.swap(None) };
                }
                if set_filename {
                    let _ = unsafe { exc.filename.swap(Some(third_arg.clone())) };
                }
            }
            #[cfg(windows)]
            if 4 <= len {
                let winerror = new_args.args.get(3).cloned();
                // Store original winerror
                let _ = unsafe { exc.winerror.swap(winerror.clone()) };

                // Convert winerror to errno and update errno + args[0]
                if let Some(errno) = winerror
                    .as_ref()
                    .and_then(|w| w.downcast_ref::<crate::builtins::PyInt>())
                    .and_then(|w| w.try_to_primitive::<i32>(vm).ok())
                    .map(crate::host_env::os::winerror_to_errno)
                {
                    let errno_obj = vm.new_pyobj(errno);
                    let _ = unsafe { exc.errno.swap(Some(errno_obj.clone())) };
                    new_args.args[0] = errno_obj;
                }
            }
        }

        // A second filename, and the two arguments the rest are cut back
        // to, both follow the filename itself having been taken.
        let has_filename = exc
            .filename
            .load_owned()
            .as_ref()
            .is_some_and(|f| !vm.is_none(f));
        if (3..=5).contains(&len) && has_filename {
            if let Some(filename2) = new_args.args.get(4)
                && !vm.is_none(filename2)
            {
                let _ = unsafe { exc.filename2.swap(Some(filename2.clone())) };
            }
            new_args.args.truncate(2);
        }
        PyBaseException::slot_init(zelf, new_args, vm)
    }

    impl Initializer for PyOSError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            if !oserror_use_init(zelf.class()) {
                return Ok(());
            }
            if !args.kwargs.is_empty() {
                return Err(vm.new_type_error(format!(
                    "{}() takes no keyword arguments",
                    zelf.class().slot_name()
                )));
            }
            oserror_init(zelf, args, vm)
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PyOSError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let obj = zelf;

            // Get OSError fields directly
            let errno_field = obj.get_attr("errno", vm).ok().filter(|v| !vm.is_none(v));
            let strerror = obj.get_attr("strerror", vm).ok().filter(|v| !vm.is_none(v));
            let filename = obj.get_attr("filename", vm).ok().filter(|v| !vm.is_none(v));
            let filename2 = obj
                .get_attr("filename2", vm)
                .ok()
                .filter(|v| !vm.is_none(v));
            #[cfg(windows)]
            let winerror = obj.get_attr("winerror", vm).ok().filter(|v| !vm.is_none(v));

            // Windows: winerror takes priority over errno
            #[cfg(windows)]
            if let Some(ref win_err) = winerror {
                let code = win_err.str(vm)?;
                if let Some(ref f) = filename {
                    let msg = strerror
                        .as_ref()
                        .map(|s| s.str(vm))
                        .transpose()?
                        .map_or_else(|| "None".to_owned(), |s| s.to_string());

                    if let Some(ref f2) = filename2 {
                        return Ok(vm.ctx.new_str(format!(
                            "[WinError {}] {}: {} -> {}",
                            code,
                            msg,
                            f.repr(vm)?,
                            f2.repr(vm)?
                        )));
                    }
                    return Ok(vm.ctx.new_str(format!(
                        "[WinError {}] {}: {}",
                        code,
                        msg,
                        f.repr(vm)?
                    )));
                }
                // winerror && strerror (no filename)
                if let Some(ref s) = strerror {
                    return Ok(vm
                        .ctx
                        .new_str(format!("[WinError {}] {}", code, s.str(vm)?)));
                }
            }

            // Non-Windows or fallback: use errno
            if let Some(ref f) = filename {
                let errno_str = errno_field
                    .as_ref()
                    .map(|e| e.str(vm))
                    .transpose()?
                    .map_or_else(|| "None".to_owned(), |s| s.to_string());
                let msg = strerror
                    .as_ref()
                    .map(|s| s.str(vm))
                    .transpose()?
                    .map_or_else(|| "None".to_owned(), |s| s.to_string());
                if let Some(ref f2) = filename2 {
                    return Ok(vm.ctx.new_str(format!(
                        "[Errno {}] {}: {} -> {}",
                        errno_str,
                        msg,
                        f.repr(vm)?,
                        f2.repr(vm)?
                    )));
                }
                return Ok(vm.ctx.new_str(format!(
                    "[Errno {}] {}: {}",
                    errno_str,
                    msg,
                    f.repr(vm)?
                )));
            }

            // errno && strerror (no filename)
            if let (Some(e), Some(s)) = (&errno_field, &strerror) {
                return Ok(vm
                    .ctx
                    .new_str(format!("[Errno {}] {}", e.str(vm)?, s.str(vm)?)));
            }

            // fallback to BaseException.__str__
            let base: &Py<PyBaseException> =
                zelf.downcast_ref().expect("OSError is a BaseException");
            Ok(base.__str__(vm))
        }

        #[pymethod]
        fn __reduce__(zelf: &Py<Self>, vm: &VirtualMachine) -> PyTupleRef {
            let base: &Py<PyBaseException> = zelf
                .as_object()
                .downcast_ref()
                .expect("OSError is a BaseException");
            let args = base.args();
            let obj = zelf.as_object().to_owned();
            let mut result: Vec<PyObjectRef> = vec![obj.class().to_owned().into()];

            if args.as_slice().len() >= 2 && args.as_slice().len() <= 5 {
                // SAFETY: len() == 2 is checked so get_arg 1 or 2 won't panic
                let errno = base.get_arg(0).expect("args len checked");
                let msg = base.get_arg(1).expect("args len checked");

                if let Ok(filename) = obj.get_attr("filename", vm) {
                    if !vm.is_none(&filename) {
                        let mut args_reduced: Vec<PyObjectRef> = vec![errno, msg, filename];

                        let filename2 = obj
                            .get_attr("filename2", vm)
                            .ok()
                            .filter(|f| !vm.is_none(f));

                        let winerror: Option<PyObjectRef> = cfg_select! {
                            windows => obj.get_attr("winerror", vm).ok().filter(|w| !vm.is_none(w)),
                            _ => None,
                        };

                        if let Some(filename2) = filename2 {
                            #[allow(clippy::unnecessary_literal_unwrap)]
                            let winerror = winerror.unwrap_or_else(|| vm.ctx.none());
                            args_reduced.extend([winerror, filename2]);
                        } else {
                            // Diverges from CPython: include winerror even without
                            // filename2 so it survives pickle round-trips.
                            if let Some(winerror) = winerror {
                                args_reduced.push(winerror);
                            }
                        }
                        result.push(args_reduced.into_pytuple(vm).into());
                    } else {
                        // filename is None - use original args as-is
                        // (may contain winerror at position 3)
                        result.push(args.into());
                    }
                } else {
                    result.push(args.into());
                }
            } else {
                result.push(args.into());
            }

            if let Some(dict) = obj.dict().filter(|x| !x.is_empty()) {
                result.push(dict.into());
            }
            result.into_pytuple(vm)
        }

        #[pygetset]
        fn characters_written(zelf: &Py<Self>, vm: &VirtualMachine) -> PyResult<isize> {
            let written = zelf.written.load();
            if written == -1 {
                Err(vm.new_attribute_error("characters_written"))
            } else {
                Ok(written)
            }
        }

        #[pygetset(setter)]
        fn set_characters_written(
            zelf: &Py<Self>,
            value: PySetterValue,
            vm: &VirtualMachine,
        ) -> PyResult<()> {
            match value {
                PySetterValue::Delete => {
                    if zelf.written.load() == -1 {
                        Err(vm.new_attribute_error("characters_written"))
                    } else {
                        zelf.written.store(-1);
                        Ok(())
                    }
                }
                PySetterValue::Assign(v) => {
                    let n = v
                        .try_index(vm)?
                        .try_to_primitive::<isize>(vm)
                        .map_err(|_| {
                            vm.new_value_error("cannot convert characters_written value to isize")
                        })?;
                    zelf.written.store(n);
                    Ok(())
                }
            }
        }
    }

    #[pyexception(name, base = PyOSError, ctx = "blocking_io_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyBlockingIOError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "child_process_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyChildProcessError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "connection_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyConnectionError(PyOSError);

    #[pyexception(name, base = PyConnectionError, ctx = "broken_pipe_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyBrokenPipeError(PyConnectionError);

    #[pyexception(
        name,
        base = PyConnectionError,
        ctx = "connection_aborted_error",
        impl
    )]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyConnectionAbortedError(PyConnectionError);

    #[pyexception(
        name,
        base = PyConnectionError,
        ctx = "connection_refused_error",
        impl
    )]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyConnectionRefusedError(PyConnectionError);

    #[pyexception(name, base = PyConnectionError, ctx = "connection_reset_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyConnectionResetError(PyConnectionError);

    #[pyexception(name, base = PyOSError, ctx = "file_exists_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyFileExistsError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "file_not_found_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyFileNotFoundError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "interrupted_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyInterruptedError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "is_a_directory_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyIsADirectoryError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "not_a_directory_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyNotADirectoryError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "permission_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyPermissionError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "process_lookup_error", impl)]
    #[repr(transparent)]
    #[derive(Debug)]
    pub struct PyProcessLookupError(PyOSError);

    #[pyexception(name, base = PyOSError, ctx = "timeout_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyTimeoutError(PyOSError);

    #[pyexception(name, base = PyException, ctx = "reference_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyReferenceError(PyException);

    #[pyexception(name, base = PyException, ctx = "runtime_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyRuntimeError(PyException);

    #[pyexception(name, base = PyRuntimeError, ctx = "not_implemented_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyNotImplementedError(PyRuntimeError);

    #[pyexception(name, base = PyRuntimeError, ctx = "recursion_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyRecursionError(PyRuntimeError);

    #[pyexception(name, base = PyRuntimeError, ctx = "python_finalization_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyPythonFinalizationError(PyRuntimeError);

    #[pyexception(name, base = PyException, ctx = "syntax_error", traverse = "manual")]
    #[repr(C)]
    pub struct PySyntaxError {
        base: PyException,
        #[pymember(writable)]
        msg: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        filename: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        lineno: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        offset: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        text: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        end_lineno: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        end_offset: PyAtomicRef<Option<PyObject>>,
        #[pymember(writable)]
        print_file_and_line: PyAtomicRef<Option<PyObject>>,
        #[pymember(name = "_metadata", writable)]
        metadata: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PySyntaxError {
        type Base = PyException;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PySyntaxError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PySyntaxError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PySyntaxError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.traverse(tracer_fn);
            for cell in [
                &self.msg,
                &self.filename,
                &self.lineno,
                &self.offset,
                &self.text,
                &self.end_lineno,
                &self.end_offset,
                &self.print_file_and_line,
                &self.metadata,
            ] {
                if let Some(obj) = cell.deref() {
                    tracer_fn(obj);
                }
            }
        }
    }

    impl Constructor for PySyntaxError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            Ok(Self {
                base: PyException(PyBaseException::new(args.args, vm)),
                msg: None.into(),
                filename: None.into(),
                lineno: None.into(),
                offset: None.into(),
                text: None.into(),
                end_lineno: None.into(),
                end_offset: None.into(),
                print_file_and_line: None.into(),
                metadata: None.into(),
            })
        }
    }

    #[pyexception(with(Constructor, Initializer))]
    impl PySyntaxError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("slot wrapper checked SyntaxError");
            fn basename(filename: &Wtf8) -> &Wtf8 {
                let bytes = filename.as_bytes();
                let pos = if cfg!(windows) {
                    bytes.iter().rposition(|&b| b == b'/' || b == b'\\')
                } else {
                    bytes.iter().rposition(|&b| b == b'/')
                };
                match pos {
                    // SAFETY: splitting at ASCII byte boundary preserves WTF-8 validity
                    Some(pos) => unsafe { Wtf8::from_bytes_unchecked(&bytes[pos + 1..]) },
                    None => filename,
                }
            }

            let maybe_lineno = exc
                .lineno
                .load_owned()
                .filter(|obj| obj.class().is(vm.ctx.types.int_type))
                .and_then(|obj| {
                    obj.downcast_ref::<PyInt>()
                        .map(|int| int.as_bigint().to_string())
                });
            let maybe_filename = exc
                .filename
                .load_owned()
                .filter(|obj| obj.fast_isinstance(vm.ctx.types.str_type))
                .map(|obj| {
                    obj.str(vm)
                        .unwrap_or_else(|_| vm.ctx.new_str("<filename str() failed>"))
                });

            let msg = match exc.msg.load_owned() {
                Some(obj) => obj
                    .str(vm)
                    .unwrap_or_else(|_| vm.ctx.new_str("<msg str() failed>")),
                None => vm.ctx.none().str(vm)?,
            };

            let msg_with_location_info: Wtf8Buf = match (maybe_lineno, maybe_filename) {
                (Some(lineno), Some(filename)) => wtf8_concat!(
                    msg.as_wtf8(),
                    " (",
                    basename(filename.as_wtf8()),
                    ", line ",
                    lineno.as_str(),
                    ")"
                ),
                (Some(lineno), None) => {
                    wtf8_concat!(msg.as_wtf8(), " (line ", lineno.as_str(), ")")
                }
                (None, Some(filename)) => {
                    wtf8_concat!(msg.as_wtf8(), " (", basename(filename.as_wtf8()), ")")
                }
                (None, None) => msg.as_wtf8().to_owned(),
            };

            Ok(vm.ctx.new_str(msg_with_location_info))
        }
    }

    impl Initializer for PySyntaxError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            let len = args.args.len();
            let new_args = args;

            let mut filename = None;
            let mut lineno = None;
            let mut offset = None;
            let mut text = None;
            let mut end_lineno = None;
            let mut end_offset = None;
            let mut metadata = None;

            let have_location = if len == 2
                && let Ok(location_tuple) = new_args.args[1]
                    .clone()
                    .downcast::<crate::builtins::PyTuple>()
            {
                let location_tup_len = location_tuple.as_slice().len();

                match location_tup_len {
                    4 | 6 | 7 => {}
                    5 => {
                        return Err(vm.new_type_error(
                            "end_offset must be provided when end_lineno is provided",
                        ));
                    }
                    given if given < 4 => {
                        return Err(vm.new_type_error(format!(
                            "function takes at least 4 arguments ({given} given)"
                        )));
                    }
                    given => {
                        return Err(vm.new_type_error(format!(
                            "function takes at most 7 arguments ({given} given)"
                        )));
                    }
                }

                let at = |index: usize| -> Option<PyObjectRef> {
                    (location_tup_len > index).then(|| location_tuple.as_slice()[index].to_owned())
                };
                filename = at(0);
                lineno = at(1);
                offset = at(2);
                text = at(3);
                end_lineno = at(4);
                end_offset = at(5);
                metadata = at(6);
                true
            } else {
                false
            };

            PyBaseException::slot_init(zelf, new_args, vm)?;
            let exc: &Py<Self> = zelf
                .downcast_ref()
                .expect("SyntaxError instance has SyntaxError payload");
            if len >= 1 {
                exc.msg.swap_to_temporary_refs(
                    Some(exc.base.0.get_arg(0).expect("args len >= 1")),
                    vm,
                );
            }
            exc.print_file_and_line
                .swap_to_temporary_refs(Some(vm.ctx.none()), vm);
            if have_location {
                exc.filename.swap_to_temporary_refs(filename, vm);
                exc.lineno.swap_to_temporary_refs(lineno, vm);
                exc.offset.swap_to_temporary_refs(offset, vm);
                exc.text.swap_to_temporary_refs(text, vm);
                exc.end_lineno.swap_to_temporary_refs(end_lineno, vm);
                exc.end_offset.swap_to_temporary_refs(end_offset, vm);
                exc.metadata.swap_to_temporary_refs(metadata, vm);
            }
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    // MiddlingExtendsException: inherits __init__ from SyntaxError via MRO
    #[pyexception(
        name = "_IncompleteInputError",
        base = PySyntaxError,
        ctx = "incomplete_input_error",
        impl
    )]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyIncompleteInputError(PySyntaxError);

    #[pyexception(name, base = PySyntaxError, ctx = "indentation_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyIndentationError(PySyntaxError);

    #[pyexception(name, base = PyIndentationError, ctx = "tab_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyTabError(PyIndentationError);

    #[pyexception(name, base = PyException, ctx = "system_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PySystemError(PyException);

    #[pyexception(name, base = PyException, ctx = "type_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyTypeError(PyException);

    #[pyexception(name, base = PyException, ctx = "value_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyValueError(PyException);

    /// Check the fixed arity expected by the tuple parser before converting
    /// any of the values it was given.
    fn parse_tuple_arity(args: &FuncArgs, count: usize, vm: &VirtualMachine) -> PyResult<()> {
        let given = args.args.len();
        if given == count {
            return Ok(());
        }
        Err(vm.new_type_error(format!(
            "function takes exactly {count} arguments ({given} given)"
        )))
    }

    fn unicode_error_payload(exc: &PyObject) -> &Py<PyUnicodeError> {
        exc.downcast_ref()
            .expect("slot wrapper checked the unicode error type")
    }

    /// `PyObject_Str` of a nullable object member. A null pointer stringifies
    /// as `<NULL>`; a stored object uses its own `__str__`.
    fn unicode_cell_str(
        cell: &PyAtomicRef<Option<PyObject>>,
        vm: &VirtualMachine,
    ) -> PyResult<PyStrRef> {
        match cell.load_owned() {
            Some(obj) => obj.str(vm),
            None => Ok(vm.ctx.new_str("<NULL>")),
        }
    }

    fn unicode_error_object(
        exc: &Py<PyUnicodeError>,
        as_bytes: bool,
        vm: &VirtualMachine,
    ) -> PyResult<PyObjectRef> {
        let Some(obj) = exc.object.load_owned() else {
            return Err(vm.new_type_error("UnicodeError 'object' attribute is not set"));
        };
        let ok = if as_bytes {
            obj.fast_isinstance(vm.ctx.types.bytes_type)
        } else {
            obj.fast_isinstance(vm.ctx.types.str_type)
        };
        if !ok {
            let kind = if as_bytes { "bytes" } else { "string" };
            return Err(
                vm.new_type_error(format!("UnicodeError 'object' attribute must be a {kind}"))
            );
        }
        Ok(obj)
    }

    #[pyexception(name, base = PyValueError, ctx = "unicode_error", traverse = "manual")]
    #[repr(C)]
    pub struct PyUnicodeError {
        base: PyValueError,
        encoding: PyAtomicRef<Option<PyObject>>,
        object: PyAtomicRef<Option<PyObject>>,
        start: AtomicIsize,
        end: AtomicIsize,
        reason: PyAtomicRef<Option<PyObject>>,
    }

    impl crate::class::PySubclass for PyUnicodeError {
        type Base = PyValueError;
        fn as_base(&self) -> &Self::Base {
            &self.base
        }
    }

    impl core::fmt::Debug for PyUnicodeError {
        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
            f.debug_struct("PyUnicodeError").finish_non_exhaustive()
        }
    }

    unsafe impl Traverse for PyUnicodeError {
        fn traverse(&self, tracer_fn: &mut TraverseFn<'_>) {
            self.base.0.0.traverse(tracer_fn);
            if let Some(obj) = self.encoding.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.object.deref() {
                tracer_fn(obj);
            }
            if let Some(obj) = self.reason.deref() {
                tracer_fn(obj);
            }
        }
    }

    fn store_unicode_error(
        zelf: &PyObject,
        encoding: Option<PyObjectRef>,
        object: Option<PyObjectRef>,
        start: isize,
        end: isize,
        reason: Option<PyObjectRef>,
        vm: &VirtualMachine,
    ) {
        let exc: &Py<PyUnicodeError> = zelf
            .downcast_ref()
            .expect("unicode error subclass has PyUnicodeError payload");
        exc.encoding.swap_to_temporary_refs(encoding, vm);
        exc.object.swap_to_temporary_refs(object, vm);
        exc.start.store(start, Ordering::Relaxed);
        exc.end.store(end, Ordering::Relaxed);
        exc.reason.swap_to_temporary_refs(reason, vm);
    }

    #[pyexception(with(Constructor))]
    impl PyUnicodeError {}

    impl Constructor for PyUnicodeError {
        type Args = FuncArgs;

        fn py_new(_cls: &Py<PyType>, args: FuncArgs, vm: &VirtualMachine) -> PyResult<Self> {
            Ok(Self {
                base: PyValueError(PyException(PyBaseException::new(args.args, vm))),
                encoding: None.into(),
                object: None.into(),
                start: AtomicIsize::new(0),
                end: AtomicIsize::new(0),
                reason: None.into(),
            })
        }
    }

    #[pyexception(name, base = PyUnicodeError, ctx = "unicode_decode_error")]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUnicodeDecodeError(
        #[pymember(name = "encoding", path = "encoding", writable)]
        #[pymember(name = "object", path = "object", writable)]
        #[pymember(name = "start", path = "start", writable)]
        #[pymember(name = "end", path = "end", writable)]
        #[pymember(name = "reason", path = "reason", writable)]
        PyUnicodeError,
    );

    #[pyexception(with(Initializer))]
    impl PyUnicodeDecodeError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let payload = unicode_error_payload(zelf);
            if payload.object.deref().is_none() {
                return Ok(vm.ctx.empty_str.to_owned());
            }
            let reason = unicode_cell_str(&payload.reason, vm)?;
            let encoding = unicode_cell_str(&payload.encoding, vm)?;
            let object: ArgBytesLike =
                unicode_error_object(payload, true, vm)?.try_into_value(vm)?;
            let start = payload.start.load(Ordering::Relaxed);
            let end = payload.end.load(Ordering::Relaxed);
            let start_u = usize::try_from(start).ok();
            let end_u = usize::try_from(end).ok();
            Ok(vm.ctx.new_str(
                if let (Some(start_u), Some(end_u)) = (start_u, end_u)
                    && start_u < object.len()
                    && end_u <= object.len()
                    && end_u == start_u + 1
                {
                    let b = object.borrow_buf()[start_u];
                    format!(
                        "'{encoding}' codec can't decode byte {b:#04x} in position {start}: {reason}"
                    )
                } else {
                    format!(
                        "'{encoding}' codec can't decode bytes in position {start}-{}: {reason}",
                        end - 1,
                    )
                },
            ))
        }
    }

    impl Initializer for PyUnicodeDecodeError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            parse_tuple_arity(&args, 5, vm)?;
            type Args = (PyStrRef, ArgBytesLike, isize, isize, PyStrRef);
            let (encoding, object, start, end, reason): Args = args.bind(vm)?;
            store_unicode_error(
                zelf,
                Some(encoding.into()),
                Some(vm.ctx.new_bytes(object.borrow_buf().to_vec()).into()),
                start,
                end,
                Some(reason.into()),
                vm,
            );
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(name, base = PyUnicodeError, ctx = "unicode_encode_error")]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUnicodeEncodeError(
        #[pymember(name = "encoding", path = "encoding", writable)]
        #[pymember(name = "object", path = "object", writable)]
        #[pymember(name = "start", path = "start", writable)]
        #[pymember(name = "end", path = "end", writable)]
        #[pymember(name = "reason", path = "reason", writable)]
        PyUnicodeError,
    );

    #[pyexception(with(Initializer))]
    impl PyUnicodeEncodeError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let payload = unicode_error_payload(zelf);
            if payload.object.deref().is_none() {
                return Ok(vm.ctx.empty_str.to_owned());
            }
            let reason = unicode_cell_str(&payload.reason, vm)?;
            let encoding = unicode_cell_str(&payload.encoding, vm)?;
            let object: PyStrRef = unicode_error_object(payload, false, vm)?.try_into_value(vm)?;
            let start = payload.start.load(Ordering::Relaxed);
            let end = payload.end.load(Ordering::Relaxed);
            let start_u = usize::try_from(start).ok();
            let end_u = usize::try_from(end).ok();
            Ok(vm.ctx.new_str(
                if let (Some(start_u), Some(end_u)) = (start_u, end_u)
                    && start_u < object.char_len()
                    && end_u <= object.char_len()
                    && end_u == start_u + 1
                {
                    let ch = object.as_wtf8().code_points().nth(start_u).unwrap();
                    format!(
                        "'{encoding}' codec can't encode character '{}' in position {start}: {reason}",
                        UnicodeEscapeCodepoint(ch)
                    )
                } else {
                    format!(
                        "'{encoding}' codec can't encode characters in position {start}-{}: {reason}",
                        end - 1,
                    )
                },
            ))
        }
    }

    impl Initializer for PyUnicodeEncodeError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            parse_tuple_arity(&args, 5, vm)?;
            type Args = (PyStrRef, PyStrRef, isize, isize, PyStrRef);
            let (encoding, object, start, end, reason): Args = args.bind(vm)?;
            store_unicode_error(
                zelf,
                Some(encoding.into()),
                Some(object.into()),
                start,
                end,
                Some(reason.into()),
                vm,
            );
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    #[pyexception(name, base = PyUnicodeError, ctx = "unicode_translate_error")]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUnicodeTranslateError(
        #[pymember(name = "encoding", path = "encoding", writable)]
        #[pymember(name = "object", path = "object", writable)]
        #[pymember(name = "start", path = "start", writable)]
        #[pymember(name = "end", path = "end", writable)]
        #[pymember(name = "reason", path = "reason", writable)]
        PyUnicodeError,
    );

    #[pyexception(with(Initializer))]
    impl PyUnicodeTranslateError {
        #[pyslot]
        fn slot_str(zelf: &PyObject, vm: &VirtualMachine) -> PyResult<PyStrRef> {
            let payload = unicode_error_payload(zelf);
            if payload.object.deref().is_none() {
                return Ok(vm.ctx.empty_str.to_owned());
            }
            let reason = unicode_cell_str(&payload.reason, vm)?;
            let object: PyStrRef = unicode_error_object(payload, false, vm)?.try_into_value(vm)?;
            let start = payload.start.load(Ordering::Relaxed);
            let end = payload.end.load(Ordering::Relaxed);
            let start_u = usize::try_from(start).ok();
            let end_u = usize::try_from(end).ok();
            Ok(vm.ctx.new_str(
                if let (Some(start_u), Some(end_u)) = (start_u, end_u)
                    && start_u < object.char_len()
                    && end_u <= object.char_len()
                    && end_u == start_u + 1
                {
                    let ch = object.as_wtf8().code_points().nth(start_u).unwrap();
                    format!(
                        "can't translate character '{}' in position {start}: {reason}",
                        UnicodeEscapeCodepoint(ch)
                    )
                } else {
                    format!(
                        "can't translate characters in position {start}-{}: {reason}",
                        end - 1,
                    )
                },
            ))
        }
    }

    impl Initializer for PyUnicodeTranslateError {
        type Args = FuncArgs;

        fn slot_init(zelf: &PyObject, args: FuncArgs, vm: &VirtualMachine) -> PyResult<()> {
            parse_tuple_arity(&args, 4, vm)?;
            type Args = (PyStrRef, isize, isize, PyStrRef);
            let (object, start, end, reason): Args = args.bind(vm)?;
            store_unicode_error(
                zelf,
                None,
                Some(object.into()),
                start,
                end,
                Some(reason.into()),
                vm,
            );
            Ok(())
        }

        fn init(_zelf: &Py<Self>, _args: Self::Args, _vm: &VirtualMachine) -> PyResult<()> {
            unreachable!("slot_init is defined")
        }
    }

    // JIT error.
    #[cfg(feature = "jit")]
    #[pyexception(name, base = PyException, ctx = "jit_error", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyJitError(PyException);

    // Warnings
    #[pyexception(name, base = PyException, ctx = "warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyWarning(PyException);

    #[pyexception(name, base = PyWarning, ctx = "deprecation_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyDeprecationWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "pending_deprecation_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyPendingDeprecationWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "runtime_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyRuntimeWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "syntax_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PySyntaxWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "user_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUserWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "future_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyFutureWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "import_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyImportWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "unicode_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyUnicodeWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "bytes_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyBytesWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "resource_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyResourceWarning(PyWarning);

    #[pyexception(name, base = PyWarning, ctx = "encoding_warning", impl)]
    #[derive(Debug)]
    #[repr(transparent)]
    pub struct PyEncodingWarning(PyWarning);
}

/// Check if match_type is valid for except* (must be exception type, not ExceptionGroup).
fn check_except_star_type_valid(match_type: &PyObject, vm: &VirtualMachine) -> PyResult<()> {
    let base_exc: PyObjectRef = vm.ctx.exceptions.base_exception_type.to_owned().into();
    let base_eg: PyObjectRef = vm.ctx.exceptions.base_exception_group.to_owned().into();

    // Helper to check a single type
    let check_one = |exc_type: &PyObject| -> PyResult<()> {
        // Must be a subclass of BaseException
        if !exc_type.is_subclass(&base_exc, vm)? {
            return Err(vm.new_type_error(
                "catching classes that do not inherit from BaseException is not allowed",
            ));
        }
        // Must not be a subclass of BaseExceptionGroup
        if exc_type.is_subclass(&base_eg, vm)? {
            return Err(vm.new_type_error(
                "catching ExceptionGroup with except* is not allowed. Use except instead.",
            ));
        }
        Ok(())
    };

    // If it's a tuple, check each element
    if let Ok(tuple) = match_type.to_owned().downcast::<PyTuple>() {
        for item in tuple.as_slice() {
            check_one(item)?;
        }
    } else {
        check_one(match_type)?;
    }
    Ok(())
}

/// Match exception against except* handler type.
/// Returns (rest, match) tuple.
pub fn exception_group_match(
    exc_value: &PyObject,
    match_type: &PyObject,
    vm: &VirtualMachine,
) -> PyResult<(PyObjectRef, PyObjectRef)> {
    // Implements _PyEval_ExceptionGroupMatch

    // If exc_value is None, return (None, None)
    if vm.is_none(exc_value) {
        return Ok((vm.ctx.none(), vm.ctx.none()));
    }

    // Validate match_type and reject ExceptionGroup/BaseExceptionGroup
    check_except_star_type_valid(match_type, vm)?;

    // Check if exc_value matches match_type
    if exc_value.is_instance(match_type, vm)? {
        // Full match of exc itself
        let is_eg = exc_value.fast_isinstance(vm.ctx.exceptions.base_exception_group);
        let matched = if is_eg {
            exc_value.to_owned()
        } else {
            // Naked exception - wrap it in ExceptionGroup
            let excs = vm.ctx.new_tuple(vec![exc_value.to_owned()]);
            let eg_type: PyObjectRef = crate::exception_group::exception_group().to_owned().into();
            let wrapped = eg_type.call((vm.ctx.new_str(""), excs), vm)?;
            // Copy traceback from original exception
            if let Ok(exc) = exc_value.to_owned().downcast::<types::PyBaseException>()
                && let Some(tb) = exc.traceback()
                && let Ok(wrapped_exc) = wrapped.clone().downcast::<types::PyBaseException>()
            {
                wrapped_exc.set_traceback(Some(tb));
            }
            wrapped
        };
        return Ok((vm.ctx.none(), matched));
    }

    // Check for partial match if it's an exception group
    if exc_value.fast_isinstance(vm.ctx.exceptions.base_exception_group) {
        let pair = vm.call_method(exc_value, "split", (match_type.to_owned(),))?;
        if !pair.class().is(vm.ctx.types.tuple_type) {
            return Err(vm.new_type_error(format!(
                "{}.split must return a tuple, not {}",
                exc_value.class().name(),
                pair.class().name()
            )));
        }
        let pair_tuple: PyTupleRef = pair.try_into_value(vm)?;
        if pair_tuple.as_slice().len() < 2 {
            return Err(vm.new_type_error(format!(
                "{}.split must return a 2-tuple, got tuple of size {}",
                exc_value.class().name(),
                pair_tuple.as_slice().len()
            )));
        }
        let matched = pair_tuple.as_slice()[0].clone();
        let rest = pair_tuple.as_slice()[1].clone();
        return Ok((rest, matched));
    }

    // No match
    Ok((exc_value.to_owned(), vm.ctx.none()))
}

/// Prepare exception for reraise in except* block.
/// Implements _PyExc_PrepReraiseStar
pub fn prep_reraise_star(orig: &PyObject, excs: &PyObject, vm: &VirtualMachine) -> PyResult {
    use crate::builtins::PyList;

    let excs_list = excs
        .downcast_ref::<PyList>()
        .ok_or_else(|| vm.new_type_error("expected list for prep_reraise_star"))?;

    let excs_vec: Vec<PyObjectRef> = excs_list.borrow_vec().to_vec();

    // If no exceptions to process, return None
    if excs_vec.is_empty() {
        return Ok(vm.ctx.none());
    }

    // Special case: naked exception (not an ExceptionGroup)
    // Only one except* clause could have executed, so there's at most one exception to raise
    if !orig.fast_isinstance(vm.ctx.exceptions.base_exception_group) {
        // Find first non-None exception
        let first = excs_vec.into_iter().find(|e| !vm.is_none(e));
        return Ok(first.unwrap_or_else(|| vm.ctx.none()));
    }

    // Split excs into raised (new) and reraised (from original) by comparing metadata
    let mut raised: Vec<PyObjectRef> = Vec::new();
    let mut reraised: Vec<PyObjectRef> = Vec::new();

    for exc in excs_vec {
        if vm.is_none(&exc) {
            continue;
        }
        // Check if this exception came from the original group
        if is_exception_from_orig(&exc, orig, vm) {
            reraised.push(exc);
        } else {
            raised.push(exc);
        }
    }

    // If no exceptions to reraise, return None
    if raised.is_empty() && reraised.is_empty() {
        return Ok(vm.ctx.none());
    }

    // Project reraised exceptions onto original structure to preserve nesting
    let reraised_eg = exception_group_projection(orig, &reraised, vm)?;

    // If no new raised exceptions, just return the reraised projection
    if raised.is_empty() {
        return Ok(reraised_eg);
    }

    // Combine raised with reraised_eg
    if !vm.is_none(&reraised_eg) {
        raised.push(reraised_eg);
    }

    // If only one exception, return it directly
    if raised.len() == 1 {
        return Ok(raised.into_iter().next().unwrap());
    }

    // Create new ExceptionGroup for multiple exceptions
    let excs_tuple = vm.ctx.new_tuple(raised);
    let eg_type: PyObjectRef = crate::exception_group::exception_group().to_owned().into();
    eg_type.call((vm.ctx.new_str(""), excs_tuple), vm)
}

/// Check if an exception came from the original group (for reraise detection).
/// Instead of comparing metadata (which can be modified when caught), we compare
/// leaf exception object IDs. split() preserves leaf exception identity.
fn is_exception_from_orig(exc: &PyObject, orig: &PyObject, vm: &VirtualMachine) -> bool {
    // Collect leaf exception IDs from exc
    let mut exc_leaf_ids = HashSet::new();
    collect_exception_group_leaf_ids(exc, &mut exc_leaf_ids, vm);

    if exc_leaf_ids.is_empty() {
        return false;
    }

    // Collect leaf exception IDs from orig
    let mut orig_leaf_ids = HashSet::new();
    collect_exception_group_leaf_ids(orig, &mut orig_leaf_ids, vm);

    // If ALL of exc's leaves are in orig's leaves, it's a reraise
    exc_leaf_ids.iter().all(|id| orig_leaf_ids.contains(id))
}

/// Collect all leaf exception IDs from an exception (group).
fn collect_exception_group_leaf_ids(
    exc: &PyObject,
    leaf_ids: &mut HashSet<usize>,
    vm: &VirtualMachine,
) {
    if vm.is_none(exc) {
        return;
    }

    // If not an exception group, it's a leaf - add its ID
    if !exc.fast_isinstance(vm.ctx.exceptions.base_exception_group) {
        leaf_ids.insert(exc.get_id());
        return;
    }

    // Recurse into exception group's exceptions
    if let Ok(excs_attr) = exc.get_attr("exceptions", vm)
        && let Ok(tuple) = excs_attr.downcast::<PyTuple>()
    {
        for e in tuple.as_slice() {
            collect_exception_group_leaf_ids(e, leaf_ids, vm);
        }
    }
}

/// Project orig onto keep list, preserving nested structure.
/// Returns an exception group containing only the exceptions from orig
/// that are also in the keep list.
fn exception_group_projection(
    orig: &PyObject,
    keep: &[PyObjectRef],
    vm: &VirtualMachine,
) -> PyResult {
    if keep.is_empty() {
        return Ok(vm.ctx.none());
    }

    // Collect all leaf IDs from keep list
    let mut leaf_ids = HashSet::new();
    for e in keep {
        collect_exception_group_leaf_ids(e, &mut leaf_ids, vm);
    }

    // Split orig by matching leaf IDs, preserving structure
    split_by_leaf_ids(orig, &leaf_ids, vm)
}

/// Recursively split an exception (group) by leaf IDs.
/// Returns the projection containing only matching leaves with preserved structure.
fn split_by_leaf_ids(exc: &PyObject, leaf_ids: &HashSet<usize>, vm: &VirtualMachine) -> PyResult {
    if vm.is_none(exc) {
        return Ok(vm.ctx.none());
    }

    // If not an exception group, check if it's in our set
    if !exc.fast_isinstance(vm.ctx.exceptions.base_exception_group) {
        if leaf_ids.contains(&exc.get_id()) {
            return Ok(exc.to_owned());
        }
        return Ok(vm.ctx.none());
    }

    // Exception group - recurse and reconstruct
    let excs_attr = exc.get_attr("exceptions", vm)?;
    let tuple: PyTupleRef = excs_attr.try_into_value(vm)?;

    let mut matched = Vec::new();
    for e in tuple.as_slice() {
        let m = split_by_leaf_ids(e, leaf_ids, vm)?;
        if !vm.is_none(&m) {
            matched.push(m);
        }
    }

    if matched.is_empty() {
        return Ok(vm.ctx.none());
    }

    let group = exc
        .downcast_ref::<crate::exception_group::types::PyBaseExceptionGroup>()
        .ok_or_else(|| vm.new_type_error("expected a BaseExceptionGroup"))?;
    crate::exception_group::types::derive_and_copy_attributes(group, matched, vm)
}