Skip to main content

A concrete syntax tree with AST-like properties for Python 3.5, 3.6, 3.7 and 3.8 programs.

Project description

LibCST

A Concrete Syntax Tree (CST) parser and serializer library for Python

Documentation CircleCI CodeCov PYPI PYPI Download Notebook

LibCST parses Python 3.0, 3.1, 3.3, 3.5, 3.6, 3.7 or 3.8 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.

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.

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:

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.

Installation

LibCST requires Python 3.6+ and can be easily installed using most common Python packaging tools. We recommend installing the latest stable release from PyPI with pip:

pip install libcst

Further Reading

Development

Start by setting up and activating a virtualenv:

git clone git@github.com:Instagram/LibCST.git libcst
cd libcst
python3 -m venv ../libcst-env/  # just an example, put this wherever you want
source ../libcst-env/bin/activate
pip install --upgrade pip  # optional, if you have an old system version of pip
pip install -r requirements.txt -r requirements-dev.txt
# If you're done with the virtualenv, you can leave it by running:
deactivate

We use isort and black to format code. To format changes to be conformant, run the following in the root:

tox -e autofix

To run all tests, you’ll need to install tox and do the following in the root:

tox -e py37

You can also run individual tests by using unittest and specifying a module like this:

python -m unitttest libcst.tests.test_batched_visitor

See the unittest documentation for more examples of how to run tests.

We use Pyre for type-checking.

To set up pyre check environment:

  1. Copy the example Pyre config: cp .pyre_configuration.example .pyre_configuration.

  2. In the config file, add your venv site-packages dir to “search_path”. (e.g. add “/workspace/libcst-env/lib/python3.7/site-packages”)

  3. Remove installed LibCST and install from the source code:

pip uninstall -y libcst
pip install -e .

To verify types for the library, do the following in the root:

pyre check

To generate documents, do the following in the root:

tox -e 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.

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.

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

libcst-0.3.4.tar.gz (380.2 kB view details)

Uploaded Source

Built Distribution

libcst-0.3.4-py3-none-any.whl (476.9 kB view details)

Uploaded Python 3

File details

Details for the file libcst-0.3.4.tar.gz.

File metadata

  • Download URL: libcst-0.3.4.tar.gz
  • Upload date:
  • Size: 380.2 kB
  • Tags: Source
  • Uploaded using Trusted Publishing? No
  • Uploaded via: twine/3.1.1 pkginfo/1.5.0.1 requests/2.23.0 setuptools/41.0.1 requests-toolbelt/0.9.1 tqdm/4.43.0 CPython/3.7.3

File hashes

Hashes for libcst-0.3.4.tar.gz
Algorithm Hash digest
SHA256 449bf67813e4ced937edb9811355e2734ac709b4f36416889c6e169a03b96362
MD5 802b493683c276b106a1c784b8ae8a51
BLAKE2b-256 7693bea24144b40f84daed08116e18d1b0163f34f3917b42fa5f6074ae4af0d7

See more details on using hashes here.

File details

Details for the file libcst-0.3.4-py3-none-any.whl.

File metadata

  • Download URL: libcst-0.3.4-py3-none-any.whl
  • Upload date:
  • Size: 476.9 kB
  • Tags: Python 3
  • Uploaded using Trusted Publishing? No
  • Uploaded via: twine/3.1.1 pkginfo/1.5.0.1 requests/2.23.0 setuptools/41.0.1 requests-toolbelt/0.9.1 tqdm/4.43.0 CPython/3.7.3

File hashes

Hashes for libcst-0.3.4-py3-none-any.whl
Algorithm Hash digest
SHA256 625feffa383da08c148539ddb879fadb4090a775d9b97463209a0864a59d4828
MD5 37942e50a4faf4b804c7a6aefbb08d8b
BLAKE2b-256 d770607e06a0122327ad281b4058551f0812630b18f6da3f638c809e9cb65024

See more details on using hashes here.

Supported by

AWS Cloud computing and Security Sponsor Datadog Monitoring Fastly CDN Google Download Analytics Pingdom Monitoring Sentry Error logging StatusPage Status page