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// Copyright (c) 2017-present PyO3 Project and Contributors
use crate::err::{PyErr, PyResult};
use crate::ffi::{self, Py_ssize_t};
use crate::{AsPyPointer, PyAny, PyObject, Python, ToPyObject};
use std::os::raw::c_long;
/// Represents a Python `slice`.
///
/// Only `c_long` indices supported at the moment by the `PySlice` object.
#[repr(transparent)]
pub struct PySlice(PyAny);
pyobject_native_type!(
PySlice,
ffi::PySliceObject,
ffi::PySlice_Type,
#checkfunction=ffi::PySlice_Check
);
/// Return value from [`PySlice::indices`].
#[derive(Debug, Eq, PartialEq)]
pub struct PySliceIndices {
/// Start of the slice
pub start: isize,
/// End of the slice
pub stop: isize,
/// Increment to use when iterating the slice from `start` to `stop`.
pub step: isize,
/// The length of the slice calculated from the original input sequence.
pub slicelength: isize,
}
impl PySliceIndices {
/// Creates a new `PySliceIndices`.
pub fn new(start: isize, stop: isize, step: isize) -> PySliceIndices {
PySliceIndices {
start,
stop,
step,
slicelength: 0,
}
}
}
impl PySlice {
/// Constructs a new slice with the given elements.
pub fn new(py: Python<'_>, start: isize, stop: isize, step: isize) -> &PySlice {
unsafe {
let ptr = ffi::PySlice_New(
ffi::PyLong_FromSsize_t(start),
ffi::PyLong_FromSsize_t(stop),
ffi::PyLong_FromSsize_t(step),
);
py.from_owned_ptr(ptr)
}
}
/// Retrieves the start, stop, and step indices from the slice object,
/// assuming a sequence of length `length`, and stores the length of the
/// slice in its `slicelength` member.
#[inline]
pub fn indices(&self, length: c_long) -> PyResult<PySliceIndices> {
// non-negative Py_ssize_t should always fit into Rust usize
unsafe {
let mut slicelength: isize = 0;
let mut start: isize = 0;
let mut stop: isize = 0;
let mut step: isize = 0;
let r = ffi::PySlice_GetIndicesEx(
self.as_ptr(),
length as Py_ssize_t,
&mut start,
&mut stop,
&mut step,
&mut slicelength,
);
if r == 0 {
Ok(PySliceIndices {
start,
stop,
step,
slicelength,
})
} else {
Err(PyErr::fetch(self.py()))
}
}
}
}
impl ToPyObject for PySliceIndices {
fn to_object(&self, py: Python<'_>) -> PyObject {
PySlice::new(py, self.start, self.stop, self.step).into()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_py_slice_new() {
Python::with_gil(|py| {
let slice = PySlice::new(py, isize::MIN, isize::MAX, 1);
assert_eq!(
slice.getattr("start").unwrap().extract::<isize>().unwrap(),
isize::MIN
);
assert_eq!(
slice.getattr("stop").unwrap().extract::<isize>().unwrap(),
isize::MAX
);
assert_eq!(
slice.getattr("step").unwrap().extract::<isize>().unwrap(),
1
);
});
}
#[test]
fn test_py_slice_indices_new() {
let start = 0;
let stop = 0;
let step = 0;
assert_eq!(
PySliceIndices::new(start, stop, step),
PySliceIndices {
start,
stop,
step,
slicelength: 0
}
);
let start = 0;
let stop = 100;
let step = 10;
assert_eq!(
PySliceIndices::new(start, stop, step),
PySliceIndices {
start,
stop,
step,
slicelength: 0
}
);
let start = 0;
let stop = -10;
let step = -1;
assert_eq!(
PySliceIndices::new(start, stop, step),
PySliceIndices {
start,
stop,
step,
slicelength: 0
}
);
let start = 0;
let stop = -10;
let step = 20;
assert_eq!(
PySliceIndices::new(start, stop, step),
PySliceIndices {
start,
stop,
step,
slicelength: 0
}
);
}
}