Pytype checks and infers types for your Python code – without requiring type
annotations. Pytype can:
- Lint plain Python code, flagging common mistakes such as mispelled attribute
names, incorrect function calls, and much more, even across
- Enforce user-provided type annotations. While annotations are
optional 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 provided
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 code
well-typed and error-free.
To quickly get started with type-checking a file or directory, run the
file_or_directory with your input:
pip install pytype pytype file_or_directory
To set up pytype on an entire package, add the following to a
in the directory immediately above the package, replacing
the package name:
[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 of a GitHub project that runs pytype on Travis.
Finally, pytype generates files of inferred type information, located by default
pytype_output/pyi. You can use this information to type-annotate the
corresponding source file, replacing
module.py with the file’s import path:
merge-pyi -i module.py pytype_output/pyi/module.pyi
You need a Python 2.7 or 3.5+ interpreter to run pytype, as well as an
$PATH for the Python version of the code you’re analyzing.
- Pytype is currently developed and tested on Linux, which is the main supported
- Installation on MacOSX requires OSX 10.7 or higher and Xcode v8 or higher.
- Windows is currently not supported.
Pytype can be installed via pip. Note that the installation requires
setuptools. (If you’re working in a virtualenv, these two packages should
already be present.)
pip install pytype
Or from the source code on GitHub.
git clone --recurse-submodules https://github.com/google/pytype.git cd pytype pip install -U .
Instead of using
--recurse-submodules, you could also have run
git submodule init git submodule update
usage: pytype [options] input [input ...] positional arguments: input file or directory to process
-V, --python-version: Python version (major.minor) of the target code.
-o, --output: The directory into which all pytype output goes, including
generated .pyi files. Defaults to
-d, --disable. Comma separated list of error names to ignore. Detailed
explanations of pytype’s error names are in this doc.
Defaults to empty.
For a full list of options, run
In addition to the above, you can direct pytype to use a custom typeshed
installation instead of its own bundled copy by setting
For convenience, you can save your pytype configuration in a file. The config
file is 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
setup.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 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
~/repo1/foo, which depends on package
~/ ├── 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
and ignore attribute errors. Notice that the path to a package does not include
the 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 by
running pytype’s broken dependency checker:
$ pytype --config=~/repo1/pytype.cfg ~/repo1/foo/*.py --unresolved Unresolved dependencies: bar.dependency
Pytype ships with three scripts in addition to
merge-pyi, for merging type information from a .pyi file into a
pytd, 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.
This is not an official Google product.