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.. 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|
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:alt: Support Ukraine - Help Provide Humanitarian Aid to Ukraine.
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.. |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 -> 3.14 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
<https://libcst.readthedocs.io/en/latest/why_libcst.html>`__ and `our
motivations for the project
<https://libcst.readthedocs.io/en/latest/motivation.html>`__
in `our documentation <https://libcst.readthedocs.io/en/latest/index.html>`__.
Try it out with `notebook examples <https://mybinder.org/v2/gh/Instagram/LibCST/main?filepath=docs%2Fsource%2Ftutorial.ipynb>`__.
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 <some_py_file.py>
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
<https://libcst.readthedocs.io/en/latest/tutorial.html>`__.
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 <https://pypi.org/project/libcst/>`_ 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 <https://rustup.rs>`_ for installing.
Further Reading
---------------
- `Static Analysis at Scale: An Instagram Story. <https://instagram-engineering.com/static-analysis-at-scale-an-instagram-story-8f498ab71a0c>`_
- `Refactoring Python with LibCST. <https://chairnerd.seatgeek.com/refactoring-python-with-libcst/>`_
Development
-----------
See `CONTRIBUTING.md <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 <https://rustup.rs/>`_.
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 <https://github.com/facebook/pyre-check>`_ 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 <LICENSE>`_, as found in the LICENSE file.
.. fb-docs-start
Privacy Policy and Terms of Use
===============================
- `Privacy Policy <https://opensource.facebook.com/legal/privacy>`_
- `Terms of Use <https://opensource.facebook.com/legal/terms>`_
.. 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.
|
