.. image:: docs/source/_static/logo/horizontal.svg :width: 600 px :alt: LibCST A Concrete Syntax Tree (CST) parser and serializer library for Python |support-ukraine| |readthedocs-badge| |ci-badge| |pypi-badge| |pypi-download| |notebook-badge| |types-badge| .. |support-ukraine| image:: https://img.shields.io/badge/Support-Ukraine-FFD500?style=flat&labelColor=005BBB :alt: Support Ukraine - Help Provide Humanitarian Aid to Ukraine. :target: https://opensource.fb.com/support-ukraine .. |readthedocs-badge| image:: https://readthedocs.org/projects/libcst/badge/?version=latest&style=flat :target: https://libcst.readthedocs.io/en/latest/ :alt: Documentation .. |ci-badge| image:: https://github.com/Instagram/LibCST/actions/workflows/build.yml/badge.svg :target: https://github.com/Instagram/LibCST/actions/workflows/build.yml?query=branch%3Amain :alt: Github Actions .. |pypi-badge| image:: https://img.shields.io/pypi/v/libcst.svg :target: https://pypi.org/project/libcst :alt: PYPI .. |pypi-download| image:: https://pepy.tech/badge/libcst/month :target: https://pepy.tech/project/libcst/month :alt: PYPI Download .. |notebook-badge| image:: https://img.shields.io/badge/notebook-run-579ACA.svg?logo=data:image/png;base64,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 :target: https://mybinder.org/v2/gh/Instagram/LibCST/main?filepath=docs%2Fsource%2Ftutorial.ipynb :alt: Notebook .. |types-badge| image:: https://img.shields.io/pypi/types/libcst :target: https://pypi.org/project/libcst :alt: PYPI - Types .. intro-start LibCST parses Python 3.0 -> 3.13 source code as a CST tree that keeps all formatting details (comments, whitespaces, parentheses, etc). It's useful for building automated refactoring (codemod) applications and linters. .. intro-end .. why-libcst-intro-start LibCST creates a compromise between an Abstract Syntax Tree (AST) and a traditional Concrete Syntax Tree (CST). By carefully reorganizing and naming node types and fields, we've created a lossless CST that looks and feels like an AST. .. why-libcst-intro-end You can learn more about `the value that LibCST provides `__ and `our motivations for the project `__ in `our documentation `__. Try it out with `notebook examples `__. Example expression:: 1 + 2 CST representation: .. code-block:: python BinaryOperation( left=Integer( value='1', lpar=[], rpar=[], ), operator=Add( whitespace_before=SimpleWhitespace( value=' ', ), whitespace_after=SimpleWhitespace( value=' ', ), ), right=Integer( value='2', lpar=[], rpar=[], ), lpar=[], rpar=[], ) Getting Started =============== Examining a sample tree ----------------------- To examine the tree that is parsed from a particular file, do the following:: python -m libcst.tool print Alternatively, you can import LibCST into a Python REPL and use the included parser and pretty printing functions: >>> import libcst as cst >>> from libcst.tool import dump >>> print(dump(cst.parse_expression("(1 + 2)"))) BinaryOperation( left=Integer( value='1', ), operator=Add(), right=Integer( value='2', ), lpar=[ LeftParen(), ], rpar=[ RightParen(), ], ) For a more detailed usage example, `see our documentation `__. Installation ------------ LibCST requires Python 3.9+ and can be easily installed using most common Python packaging tools. We recommend installing the latest stable release from `PyPI `_ with pip: .. code-block:: shell pip install libcst For parsing, LibCST ships with a native extension, so releases are distributed as binary wheels as well as the source code. If a binary wheel is not available for your system (Linux/Windows x86/x64 and Mac x64/arm are covered), you'll need a recent `Rust toolchain `_ for installing. Further Reading --------------- - `Static Analysis at Scale: An Instagram Story. `_ - `Refactoring Python with LibCST. `_ Development ----------- See `CONTRIBUTING.md `_ for more details. Building ~~~~~~~~ In order to build LibCST, which includes a native parser module, you will need to have the Rust build tool ``cargo`` on your path. You can usually install ``cargo`` using your system package manager, but the most popular way to install cargo is using `rustup `_. To build just the native parser, do the following from the ``native`` directory: .. code-block:: shell cargo build The ``libcst.native`` module should be rebuilt automatically, but to force it: .. code-block:: shell uv sync --reinstall-package libcst Type Checking ~~~~~~~~~~~~~ We use `Pyre `_ for type-checking. To verify types for the library, do the following in the root: .. code-block:: shell uv run poe typecheck Generating Documents ~~~~~~~~~~~~~~~~~~~~ To generate documents, do the following in the root: .. code-block:: shell uv run --group docs poe docs Future ====== - Advanced full repository facts providers like fully qualified name and call graph. License ======= LibCST is `MIT licensed `_, as found in the LICENSE file. .. fb-docs-start Privacy Policy and Terms of Use =============================== - `Privacy Policy `_ - `Terms of Use `_ .. fb-docs-end Acknowledgements ================ - Guido van Rossum for creating the parser generator pgen2 (originally used in lib2to3 and forked into parso). - David Halter for parso which provides the parser and tokenizer that LibCST sits on top of. - Zac Hatfield-Dodds for hypothesis integration which continues to help us find bugs. - Zach Hammer improved type annotation for Mypy compatibility.

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