Expand description

This crate can be used to parse Python source code into an Abstract Syntax Tree.


The process by which source code is parsed into an AST can be broken down into two general stages: lexical analysis and parsing.

During lexical analysis, the source code is converted into a stream of lexical tokens that represent the smallest meaningful units of the language. For example, the source code print("Hello world") would roughly be converted into the following stream of tokens:

Name("print"), LeftParen, String("Hello world"), RightParen

these tokens are then consumed by the parser, which matches them against a set of grammar rules to verify that the source code is syntactically valid and to construct an AST that represents the source code.

During parsing, the parser consumes the tokens generated by the lexer and constructs a tree representation of the source code. The tree is made up of nodes that represent the different syntactic constructs of the language. If the source code is syntactically invalid, parsing fails and an error is returned. After a successful parse, the AST can be used to perform further analysis on the source code. Continuing with the example above, the AST generated by the parser would roughly look something like this:

node: Expr {
    value: {
        node: Call {
            func: {
                node: Name {
                    id: "print",
                    ctx: Load,
            args: [
                node: Constant {
                    value: Str("Hello World"),
                    kind: None,
            keywords: [],

Note: The Tokens/ASTs shown above are not the exact tokens/ASTs generated by the parser.

§Source code layout:

The functionality of this crate is split into several modules:

  • token: This module contains the definition of the tokens that are generated by the lexer.
  • lexer: This module contains the lexer and is responsible for generating the tokens.
  • parser: This module contains an interface to the parser and is responsible for generating the AST.
    • Functions and strings have special parsing requirements that are handled in additional files.
  • mode: This module contains the definition of the different modes that the parser can be in.


For example, to get a stream of tokens from a given string, one could do this:

use rustpython_parser::{lexer::lex, Mode};

let python_source = r#"
def is_odd(i):
    return bool(i & 1)
let mut tokens = lex(python_source, Mode::Module);
assert!(tokens.all(|t| t.is_ok()));

These tokens can be directly fed into the parser to generate an AST:

use rustpython_parser::{lexer::lex, Mode, parse_tokens};

let python_source = r#"
def is_odd(i):
   return bool(i & 1)
let tokens = lex(python_source, Mode::Module);
let ast = parse_tokens(tokens, Mode::Module, "<embedded>");


Alternatively, you can use one of the other parse_* functions to parse a string directly without using a specific mode or tokenizing the source beforehand:

use rustpython_parser::{Parse, ast};

let python_source = r#"
def is_odd(i):
  return bool(i & 1)
let ast = ast::Suite::parse(python_source, "<embedded>");




  • This module takes care of lexing Python source text.
  • Newtypes for working with text sizes/ranges in a more type-safe manner.


  • Represents the different types of errors that can occur during parsing of an f-string.
  • The mode argument specifies in what way code must be parsed.
  • Represents the different types of errors that can occur during parsing.
  • The kind of string literal as described in the String and Bytes literals section of the Python reference.
  • The set of tokens the Python source code can be tokenized in.


  • Parse Python code string to implementor’s type.


Type Aliases§

  • Represents represent errors that occur during parsing and are returned by the parse_* functions.