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Pytype

Pytype checks and infers types for your Python code - without requiring typeannotations. Pytype can:

• Lint plain Python code, flagging common mistakes such as mispelled attributenames, incorrect function calls, and much more, even acrossfile boundaries.
• Enforce user-provided type annotations. While annotations areoptional for pytype, it will check and apply them where present.
• Generate type annotations in standalone files ("pyi files"),which can be merged back into the Python source with a providedmerge-pyi tool.

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

Thousands of projects at Google rely on pytype to keep their Python codewell-typed and error-free.

For more information, check out the user guide or FAQ.

Quickstart

To quickly get started with type-checking a file or directory, run thefollowing, replacing file_or_directory with your input:

pip install pytypepytype file_or_directory

To set up pytype on an entire package, add the following to a setup.cfg filein the directory immediately above the package, replacing package_name withthe package name:

[pytype]inputs = package_name

Now you can run the no-argument command pytype to type-check the package. It'salso easy to add pytype to your automated testing; see thisexample of a GitHub project that runs pytype on Travis.

Finally, pytype generates files of inferred type information, located by defaultin pytype_output/pyi. You can use this information to type-annotate thecorresponding source file, replacing module.py with the file's import path:

merge-pyi -i module.py pytype_output/pyi/module.pyi

Requirements

You need a Python 2.7 or 3.5+ interpreter to run pytype, as well as aninterpreter in $PATH for the Python version of the code you're analyzing.

Platform support:

• Pytype is currently developed and tested on Linux, which is the main supportedplatform.
• Installation on MacOSX requires OSX 10.7 or higher and Xcode v8 or higher.
• Windows is currently not supported.

Installing

Pytype can be installed via pip. Note that the installation requires wheeland setuptools. (If you're working in a virtualenv, these two packages shouldalready be present.)

pip install pytype

Or from the source code on GitHub.

git clone --recurse-submodules https://github.com/google/pytype.gitcd pytypepip install -U .

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

git submodule initgit submodule update

in the pytype directory.

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 3.6.
• -o, --output: The directory into which all pytype output goes, includinggenerated .pyi files. Defaults to pytype_output.
• -d, --disable. Comma separated list of error names to ignore. Detailedexplanations of pytype's error names are in this doc.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 typeshedinstallation instead of its own bundled copy by setting $TYPESHED_HOME.

Config File

For convenience, you can save your pytype configuration in a file. The configfile is an INI-style file with a [pytype] section; if an explicit config fileis not supplied, pytype will look for a [pytype] section in the firstsetup.cfg file found by walking upwards from the current working directory.

Start off by generating a sample config file:

$ pytype --generate-config pytype.cfg

Now customize the file based on your local setup, keeping only the sections youneed. Directories may be relative to the location of the config file, which isuseful 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 toanalyze 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 3.6 code, look for packages in ~/repo1 and ~/repo2,and ignore attribute errors. Notice that the path to a package does not includethe package itself.

```$ cat ~/repo1/pytype.cfg

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

[pytype]

Space-separated list of files or directories to process.

inputs = foo

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

python_version = 3.6

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

pythonpath = .: ~/repo2

Comma separated list of error names to ignore.

disable = attribute-error```

We could've discovered that ~/repo2 needed to be added to the pythonpath byrunning pytype's broken dependency checker:

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

Unresolved dependencies: bar.dependency```

Subtools

Pytype ships with three scripts in addition to pytype itself:

• merge-pyi, for merging type information from a .pyi file into aPython file.
• pytd, a parser for .pyi files.
• pytype-single, a debugging tool for pytype developers, which analyzes asingle Python file assuming that .pyi files have already been generated for allof its dependencies.

Roadmap

• Windows support

License

Apache 2.0

Disclaimer

This is not an official Google product.

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