Optional static typing for Python 2 and 3 (PEP484)
Python PLSQL XSLT CSS Emacs Lisp Shell
Latest commit 04a2aec Jun 22, 2017 @gvanrossum gvanrossum committed on GitHub Sync typeshed (#3586)
Failed to load latest commit information.
docs Add flag to disallow decorating functions with decorators with imprec… Jun 21, 2017
extensions Move version of extensions to post-release (#3348) May 29, 2017
misc Add script that builds packages and uploads them to PyPI (#2948) Mar 6, 2017
mypy Add flag to disallow decorating functions with decorators with imprec… Jun 21, 2017
pinfer spelling fixes (#1499) May 6, 2016
scripts Add console scripts (#3074) May 27, 2017
test-data Add flag to disallow decorating functions with decorators with imprec… Jun 21, 2017
tmp-test-dirs Allow testsuite to run in parallel Oct 11, 2015
typeshed @ 6fe68fd Sync typeshed (#3586) Jun 22, 2017
xml HTML report CSS tweaks Oct 11, 2015
.gitignore Optimize tests (parallel execution) (#3019) Apr 3, 2017
.gitmodules add typeshed, and tweak default_lib_path accordingly Sep 30, 2015
.travis.yml Remove bundled lib-typing (#3337) May 29, 2017
CONTRIBUTING.md Change python/mypy chat room to python/typing (last occurrences) (#3584) Jun 21, 2017
CREDITS Update CREDITS Feb 18, 2016
LICENSE Remove bundled lib-typing (#3337) May 29, 2017
MANIFEST.in Make typing and typed-ast external dependencies (#2452) Jan 6, 2017
README.md Change python/mypy chat room to python/typing (last occurrences) (#3584) Jun 21, 2017
ROADMAP.md Add --strict-optional on by default to roadmap (#3478) May 31, 2017
appveyor.yml Run Appveyor tests on only one architecture (#3401) May 22, 2017
build-requirements.txt Make typing and typed-ast external dependencies (#2452) Jan 6, 2017
conftest.py conftest.py: Fix lint May 23, 2017
mypy_self_check.ini More mypy test typing (#2687) Jan 13, 2017
mypy_strict_optional.ini Annotate yet more test code (#2671) Jan 10, 2017
pytest.ini pytest: Add some comments to explain pytest's magic (#3034) Mar 31, 2017
runtests.py Handle flags in pytest passthrough (#3467) May 30, 2017
setup.cfg Bump typed-ast dependency to 1.0.4. (#3545) Jun 14, 2017
setup.py Bump typed-ast dependency to 1.0.4. (#3545) Jun 14, 2017
test-requirements.txt Bump typed-ast dependency to 1.0.4. (#3545) Jun 14, 2017


Mypy: Optional Static Typing for Python

Build Status Chat at https://gitter.im/python/typing

Got a question? Join us on Gitter!

We don't have a mailing list; but we are always happy to answer questions on gitter chat. If you are sure you've found a bug please search our issue trackers for a duplicate before filing a new issue:

What is mypy?

Mypy is an optional static type checker for Python. You can add type hints to your Python programs using the standard for type annotations introduced in Python 3.5 (PEP 484), and use mypy to type check them statically. Find bugs in your programs without even running them!

The type annotation standard has also been backported to earlier Python 3.x versions. Mypy supports Python 3.3 and later.

For Python 2.7, you can add annotations as comments (this is also specified in PEP 484).

You can mix dynamic and static typing in your programs. You can always fall back to dynamic typing when static typing is not convenient, such as for legacy code.

Here is a small example to whet your appetite:

from typing import Iterator

def fib(n: int) -> Iterator[int]:
    a, b = 0, 1
    while a < n:
        yield a
        a, b = b, a + b

Mypy is in development; some features are missing and there are bugs. See 'Development status' below.


You need Python 3.3 or later to run mypy. You can have multiple Python versions (2.x and 3.x) installed on the same system without problems.

In Ubuntu, Mint and Debian you can install Python 3 like this:

$ sudo apt-get install python3 python3-pip

For other Linux flavors, OS X and Windows, packages are available at


Quick start

Mypy can be installed using pip:

$ python3 -m pip install -U mypy

If you want to run the latest version of the code, you can install from git:

$ python3 -m pip install -U git+git://github.com/python/mypy.git

Now, if Python on your system is configured properly (else see "Troubleshooting" below), you can type-check the statically typed parts of a program like this:

$ mypy PROGRAM

You can always use a Python interpreter to run your statically typed programs, even if they have type errors:

$ python3 PROGRAM

IDE & Linter Integrations

Mypy can be integrated into popular IDEs:

Mypy can also be integrated into Flake8 using flake8-mypy.

Web site and documentation

Documentation and additional information is available at the web site:


Or you can jump straight to the documentation:



Depending on your configuration, you may have to run pip3 like this:

$ python3 -m pip install -U mypy

This should automatically installed the appropriate version of mypy's parser, typed-ast. If for some reason it does not, you can install it manually:

$ python3 -m pip install -U typed-ast

If the mypy command isn't found after installation: After either pip3 install or setup.py install, the mypy script and dependencies, including the typing module, will be installed to system-dependent locations. Sometimes the script directory will not be in PATH, and you have to add the target directory to PATH manually or create a symbolic link to the script. In particular, on Mac OS X, the script may be installed under /Library/Frameworks:


In Windows, the script is generally installed in \PythonNN\Scripts. So, type check a program like this (replace \Python34 with your Python installation path):

C:\>\Python34\python \Python34\Scripts\mypy PROGRAM

Working with virtualenv

If you are using virtualenv, make sure you are running a python3 environment. Installing via pip3 in a v2 environment will not configure the environment to run installed modules from the command line.

$ python3 -m pip install -U virtualenv
$ python3 -m virtualenv env

Quick start for contributing to mypy

If you want to contribute, first clone the mypy git repository:

$ git clone --recurse-submodules https://github.com/python/mypy.git

If you've already cloned the repo without --recurse-submodules, you need to pull in the typeshed repo as follows:

$ git submodule init
$ git submodule update

Either way you should now have a subdirectory typeshed containing a clone of the typeshed repo (https://github.com/python/typeshed).

From the mypy directory, use pip to install mypy:

$ cd mypy
$ python3 -m pip install -U .

Replace python3 with your Python 3 interpreter. You may have to do the above as root. For example, in Ubuntu:

$ sudo python3 -m pip install -U .

Now you can use the mypy program just as above. In case of trouble see "Troubleshooting" above.

Working with the git version of mypy

mypy contains a submodule, "typeshed". See http://github.com/python/typeshed. This submodule contains types for the Python standard library.

Due to the way git submodules work, you'll have to do

  git submodule update typeshed

whenever you change branches, merge, rebase, or pull.

(It's possible to automate this: Search Google for "git hook update submodule")


See Test README.md

Development status

Mypy is work in progress and is not yet production quality, though mypy development has been done using mypy for a while!

Here are some of the more significant Python features not supported right now (but all of these will improve):

  • properties with setters not supported
  • limited metaclass support
  • only a subset of Python standard library modules are supported, and some only partially
  • 3rd party module support is limited

The current development focus is to have a good coverage of Python features and the standard library (both 3.x and 2.7).

Issue tracker

Please report any bugs and enhancement ideas using the mypy issue tracker:


Feel free to also ask questions on the tracker.

Help wanted

Any help in testing, development, documentation and other tasks is highly appreciated and useful to the project. There are tasks for contributors of all experience levels. If you're just getting started, check out the difficulty/easy label.

For more details, see the file CONTRIBUTING.md.


Mypy is licensed under the terms of the MIT License (see the file LICENSE).