A static analyzer for Python code
Clone or download
Latest commit 17b72a4 Dec 12, 2018
Type Name Latest commit message Commit time
Failed to load latest commit information.
2.7_patches Update the type annotations backporting patch. (#121) Aug 10, 2018
build_scripts Move pytype options out of travis_script into setup.cfg. Sep 20, 2018
cmake/modules Run the cc_test binaries when the targets are built. Aug 23, 2018
cpython @ 9734024 Add back the cpython submodule. Sep 7, 2018
docs Replace the contrived `x: 0` example with one of a function as a type… Oct 4, 2018
googletest @ e82d320 Add back the googletest submodule. (#132) Aug 17, 2018
out Move the "out" directory to the right place in the open source tree. May 18, 2018
pytype Add Python 3.7 opcode mapping. Dec 12, 2018
typeshed @ 9ee4582 Update typeshed to 9ee458226c212acc2691f014d2a5575f33160d6d. Oct 28, 2018
.gitmodules Add cpython submodule pinned to the current 2.7 HEAD. Sep 4, 2018
.travis.yml Remove custom email notification settings from .travis.yml. Nov 1, 2018
AUTHORS Add current authors and pytype alumni to AUTHORS file. Dec 22, 2017
CHANGELOG Add Python 3.7 opcode mapping. Dec 12, 2018
CMakeLists.txt Add implementations of cc_library and cc_test rules and use them. Aug 20, 2018
CONTRIBUTING.md Update CONTRIBUTING.md with info that run_tests.py also runs C++ unit… Aug 29, 2018
DESCRIPTION.rst Improve error messages for `+` and `~` operators. Dec 12, 2018
LICENSE add pytype source Mar 19, 2015
MANIFEST.in Project import generated by Copybara. Jun 29, 2018
README.md Improve error messages for `+` and `~` operators. Dec 12, 2018
setup.cfg Turn on type-checking for more of pytype itself. Oct 5, 2018
setup.py Use https as the website url scheme Dec 5, 2018


Build Status


Statically check and infer types for unannotated Python code.


Pytype is a static analyzer that helps you find type errors in Python code. It can type-check code with or without type annotations, as well as generate annotations. Pytype runs under Python 2.7 or 3.5+ and analyzes both Python 2 and Python 3 code.


Below, print_greeting calls make_greeting incorrectly:

$ cat foo.py

def make_greeting(user_id):
    return 'hello, user' + user_id

def print_greeting():

Run pytype to catch the bug:

$ pytype foo.py

File "foo.py", line 2, in make_greeting: unsupported operand type(s) for +: 'str' and 'int' [unsupported-operands]
  str.__add__ expected str
  line 5, in print_greeting

Merge pytype's generated type information back into foo.py:

$ cat pytype_output/foo.pyi

def make_greeting(user_id) -> str: ...
def print_greeting() -> None: ...

$ merge-pyi -i foo.py pytype_output/foo.pyi
$ cat foo.py

def make_greeting(user_id) -> str:
    return 'hello, user' + user_id

def print_greeting() -> None:


You need a Python 2.7 or 3.5+ interpreter to run pytype, as well as an interpreter 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 supported platform.
  • Installation on MacOSX requires OSX 10.7 or higher and Xcode v8 or higher.
  • Windows is currently not supported.

Quickstart resources

The rest of this document provides complete instructions for installing and using pytype. To quickly get started with some common workflows, check out the following docs:


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.)

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

in the pytype directory.


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, including generated .pyi files. Defaults to pytype_output.
  • -P, --pythonpath. Paths to source code directories, separated by ':'. Defaults to an educated guess based on input.
  • -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 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 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 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 3.6 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.

$ cat ~/repo1/pytype.cfg

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


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

# Python version (major.minor) of the target code.
python_version = 3.6

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

# Comma separated list of error names to ignore.
disable =

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:


Pytype ships with three scripts in addition to pytype itself:

  • merge-pyi, for merging type information from a .pyi file into a Python file.
  • 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.


  • Windows support
  • A rerun mode to only reanalyze files that have changed since the last run


Apache 2.0


This is not an official Google product.