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https://github.com/google/pytype

A static type analyzer for Python code
https://github.com/google/pytype

linter python static-analysis static-code-analysis typechecker types typing

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A static type analyzer for Python code

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# pytype - 🦆✔



Pytype checks and infers types for your Python code - without requiring type

annotations. Pytype can:



* Lint plain Python code, flagging common mistakes such as misspelled attribute

names, incorrect function calls, and [much more][error-classes], even across

file boundaries.

* Enforce user-provided [type annotations][pep-484]. While annotations are

optional for pytype, it will check and apply them where present.

* Generate type annotations in standalone files ("[pyi files][pyi-stub-files]"),

which can be merged back into the Python source with a provided

[merge-pyi][merge-pyi] tool.



Pytype is a static analyzer; it does not execute the code it runs on.



Thousands of projects at Google rely on pytype to keep their Python code

well-typed and error-free.



For more information, check out the [user guide][user-guide], [FAQ][faq], or

[supported features][supported-features].



## How is pytype different from other type checkers?



1. Pytype uses **inference** instead of gradual typing. This means it will

infer types on code even when the code has no type hints on it. So it can

detect issues with code like this, which other type checkers would miss:



    ```python

    def f():

        return "PyCon"

    def g():

        return f() + 2019



    # pytype: line 4, in g: unsupported operand type(s) for +: 'str'

    # and 'int' [unsupported-operands]

    ```



1. Pytype is **lenient** instead of strict. That means it allows all

operations that succeed at runtime and don't contradict annotations. For

instance, this code will pass as safe in pytype, but fail in other type

checkers, which assign types to variables as soon as they are initialized:



    ```python

    from typing import List

    def get_list() -> List[str]:

        lst = ["PyCon"]

        lst.append(2019)

        return [str(x) for x in lst]



    # mypy: line 4: error: Argument 1 to "append" of "list" has

    # incompatible type "int"; expected "str"

    ```



Also see the corresponding [FAQ entry][faq-diff].



## Quickstart



To quickly get started with type-checking a file or directory, run the

following, replacing `file_or_directory` with your input:



```shell

pip install pytype

pytype file_or_directory

```



To set up pytype on an entire package, add the following to a `pyproject.toml`

file in the directory immediately above the package, replacing `package_name`

with the package name:



```toml

[tool.pytype]

inputs = ['package_name']

```



Now you can run the no-argument command `pytype` to type-check the package. It's

also easy to add pytype to your automated testing; see this

[example][importlab-github-actions] of a GitHub project that runs pytype on GitHub Actions.



Finally, pytype generates files of inferred type information, located by default

in `.pytype/pyi`. You can use this information to type-annotate the

corresponding source file:



```shell

merge-pyi -i .py .pytype/pyi/.pyi

```



## Requirements



You need a Python 3.8-3.12 interpreter to run pytype, as well as an

interpreter in `$PATH` for the Python version of the code you're analyzing

(supported: 3.8-3.12).



Platform support:



* Pytype is currently developed and tested on Linux\*, which is the main supported

  platform.

* Installation on MacOSX requires OSX 10.7 or higher and Xcode v8 or higher**.

* Windows is currently not supported unless you use [WSL][wsl].



\*

On Alpine Linux, installation may fail due to issues with upstream

dependencies.  See the details of [this issue][scikit-build-issue] for a

possible fix.




\*\*

If the ninja dependency fails to install, make sure cmake is installed. See

[this issue][ninja-build-issue] for details.




## Installing



Pytype can be installed via pip. Note that the installation requires `wheel`

and `setuptools`. (If you're working in a virtualenv, these two packages should

already be present.)



```shell

pip install pytype

```



Or from the source code [on GitHub][github].



```shell

git clone --recurse-submodules https://github.com/google/pytype.git

cd pytype

pip install .

```



Instead of using `--recurse-submodules`, you could also have run



```shell

git submodule init

git submodule update

```



in the `pytype` directory. To edit the code and have your edits tracked live,

replace the pip install command with:



```shell

pip install -e .

```



### Installing on WSL



Follow the steps above, but make sure you have the correct libraries first:



```shell

sudo apt install build-essential python3-dev libpython3-dev

```



## Usage



```

usage: pytype [options] input [input ...]



positional arguments:

  input                 file or directory to process

```



Common options:



* `-V, --python-version`: Python version (major.minor) of the target code.

  Defaults to the version that pytype is running under.

* `-o, --output`: The directory into which all pytype output goes, including

  generated .pyi files. Defaults to `.pytype`.

* `-d, --disable`. Comma or space-separated list of error names to ignore.

  Detailed explanations of pytype's error names are in

  [this doc][error-classes]. Defaults to empty.



For a full list of options, run `pytype --help`.



In addition to the above, you can direct pytype to use a custom typeshed

installation instead of its own bundled copy by setting `$TYPESHED_HOME`.



### Config File



For convenience, you can save your pytype configuration in a file. The config

file can be a TOML-style file with a `[tool.pytype]` section (preferred) or an

INI-style file with a `[pytype]` section. If an explicit config file is not

supplied, pytype will look for a pytype section in the first `pyproject.toml` or

`setup.cfg` file found by walking upwards from the current working directory.



Start off by generating a sample config file:



```shell

$ pytype --generate-config pytype.toml

```



Now customize the file based on your local setup, keeping only the sections you

need. Directories may be relative to the location of the config file, which is

useful if you want to check in the config file as part of your project.



For example, suppose you have the following directory structure and want to

analyze package `~/repo1/foo`, which depends on package `~/repo2/bar`:



```

~/

├── repo1

│   └── foo

│       ├── __init__.py

│       └── file_to_check.py

└── repo2

    └── bar

        ├── __init__.py

        └── dependency.py

```



Here is the filled-in config file, which instructs pytype to type-check

`~/repo1/foo` as Python 3.9 code, look for packages in `~/repo1` and `~/repo2`,

and ignore attribute errors. Notice that the path to a package does not include

the package itself.



```toml

$ cat ~/repo1/pytype.toml



# NOTE: All relative paths are relative to the location of this file.



[tool.pytype]



# Space-separated list of files or directories to process.

inputs = [

    'foo',

]



# Python version (major.minor) of the target code.

python_version = '3.9'



# Paths to source code directories, separated by ':'.

pythonpath = .:~/repo2



# Space-separated list of error names to ignore.

disable = [

    'attribute-error',

]

```



We could've discovered that `~/repo2` needed to be added to the pythonpath by

running pytype's broken dependency checker:



```

$ pytype --config=~/repo1/pytype.toml ~/repo1/foo/*.py --unresolved



Unresolved dependencies:

  bar.dependency

```



### Subtools



Pytype ships with a few scripts in addition to `pytype` itself:



* `annotate-ast`, an in-progress type annotator for ASTs.

* [`merge-pyi`][merge-pyi], for merging type information from a .pyi file into a

Python file.

* `pytd-tool`, a parser for .pyi files.

* `pytype-single`, a debugging tool for pytype developers, which analyzes a

single Python file assuming that .pyi files have already been generated for all

of its dependencies.

* `pyxref`, a cross-references generator.



## License



[Apache 2.0][license]



## Disclaimer



This is not an official Google product.



[error-classes]: docs/errors.md

[faq]: docs/faq.md

[faq-diff]: docs/faq.md#how-is-pytype-different-from-other-type-checkers

[github]: https://github.com/google/pytype/

[importlab-github-actions]: https://github.com/google/importlab/blob/main/.github/workflows/ci.yml

[license]: https://github.com/google/pytype/blob/main/LICENSE

[merge-pyi]: https://github.com/google/pytype/tree/main/pytype/tools/merge_pyi

[ninja-build-issue]: https://github.com/google/pytype/issues/957

[pep-484]: https://www.python.org/dev/peps/pep-0484

[pyi-stub-files]: docs/user_guide.md#pyi-stub-files

[scikit-build-issue]: https://github.com/scikit-build/ninja-python-distributions/issues/27

[supported-features]: docs/support.md

[user-guide]: docs/user_guide.md

[wsl]: https://docs.microsoft.com/en-us/windows/wsl/faq