Skip to main content

A concrete syntax tree with AST-like properties for Python 3.7 programs.

Project description

LibCST

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

Documentation CircleCI CodeCov PYPI Notebook

LibCST parses Python 3.7 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.

1 + 2
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

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 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

License

LibCST is MIT licensed, as found in the LICENSE file.

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-0.1.2.tar.gz (188.0 kB view details)

Uploaded Source

Built Distribution

libcst-0.1.2-py3-none-any.whl (240.2 kB view details)

Uploaded Python 3

File details

Details for the file libcst-0.1.2.tar.gz.

File metadata

  • Download URL: libcst-0.1.2.tar.gz
  • Upload date:
  • Size: 188.0 kB
  • Tags: Source
  • Uploaded using Trusted Publishing? No
  • Uploaded via: twine/1.13.0 pkginfo/1.5.0.1 requests/2.22.0 setuptools/39.0.1 requests-toolbelt/0.9.1 tqdm/4.32.2 CPython/3.7.3

File hashes

Hashes for libcst-0.1.2.tar.gz
Algorithm Hash digest
SHA256 51c98bbab76540d1a4f12295719b4559e24957cb1e95a136a5aec9560bb7d52a
MD5 6db454c366c8682eae58af9db109a584
BLAKE2b-256 e3b7f8be0e5aa3217923a121a17d838fe99c3762ee2cab742f32d65ce3ab109a

See more details on using hashes here.

Provenance

File details

Details for the file libcst-0.1.2-py3-none-any.whl.

File metadata

  • Download URL: libcst-0.1.2-py3-none-any.whl
  • Upload date:
  • Size: 240.2 kB
  • Tags: Python 3
  • Uploaded using Trusted Publishing? No
  • Uploaded via: twine/1.13.0 pkginfo/1.5.0.1 requests/2.22.0 setuptools/39.0.1 requests-toolbelt/0.9.1 tqdm/4.32.2 CPython/3.7.3

File hashes

Hashes for libcst-0.1.2-py3-none-any.whl
Algorithm Hash digest
SHA256 1df1e013dbe296ab409b0745837e98eead4207d95eba6f13fff1a303ee8901dd
MD5 00e4e3a3c261ed92db3a42dfb3aa7b75
BLAKE2b-256 10d40390422092b4d016d610db304d014c733c53367581a5c51ac20427ed2aa7

See more details on using hashes here.

Provenance

Supported by

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