mypy

Optional static typing for Python 2 and 3 (PEP 484)

Mypy: Optional Static Typing for Python

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

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 (PEP 484) to your
Python programs, and use mypy to type check them statically.
Find bugs in your programs without even running them!

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 (Python 3):

from typing import Iterator

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

See the documentation for more examples.

For Python 2.7, the standard annotations are written as comments:

def is_palindrome(s):
    # type: (str) -> bool
    return s == s[::-1]

See the documentation for Python 2 support.

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

Requirements

You need Python 3.5 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, macOS and Windows, packages are available at

http://www.python.org/getit/

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

You can also try mypy in an online playground (developed by
Yusuke Miyazaki).

IDE, Linter Integrations, and Pre-commit

Mypy can be integrated into popular IDEs:

Mypy can also be integrated into Flake8 using flake8-mypy, or
can be set up as a pre-commit hook using pre-commit mirrors-mypy.

Web site and documentation

Documentation and additional information is available at the web site:

http://www.mypy-lang.org/

Or you can jump straight to the documentation:

http://mypy.readthedocs.io/

Troubleshooting

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

$ python3 -m pip install -U mypy

This should automatically install 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
python3 -m pip 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
macOS, the script may be installed under /Library/Frameworks:

/Library/Frameworks/Python.framework/Versions/<version>/bin

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 inside your mypy repo,
your folders tree should be like mypy/mypy/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 mypy/typeshed

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

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

Tests

The basic way to run tests:

$ pip3 install -r test-requirements.txt
$ python2 -m pip install -U typing
$ ./runtests.py

For more on the tests, such as how to write tests and how to control
which tests to run, see Test README.md.

Development status

Mypy is beta software, but it has already been used in production
for several years at Dropbox, and it has an extensive test suite.

See the roadmap if you are interested in plans for the
future.

Changelog

Follow mypy's updates on the blog: http://mypy-lang.blogspot.com/

Issue tracker

Please report any bugs and enhancement ideas using the mypy issue
tracker: https://github.com/python/mypy/issues

If you have any questions about using mypy or types, please ask
in the typing gitter instead: https://gitter.im/python/typing

Compiled version of mypy

We have built a compiled version of mypy using the mypyc
compiler
for
mypy-annotated Python code. It is approximately 4 times faster than
interpreted mypy and is available (and the default) for 64-bit
Windows, macOS, and Linux.

To install an interpreted mypy instead, use:

$ python3 -m pip install --no-binary mypy -U mypy

If you wish to test out the compiled version of a development
version of mypy, you can directly install a binary from
https://github.com/mypyc/mypy_mypyc-wheels/releases/latest.

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,
ask on the gitter chat for ideas of good
beginner issues.

For more details, see the file CONTRIBUTING.md.

License

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

主要指標

概覽
名稱與所有者python/mypy
主編程語言Python
編程語言Python (語言數: 10)
平台
許可證Other
所有者活动
創建於2012-12-07 13:30:23
推送於2025-05-20 01:39:01
最后一次提交2025-05-19 18:39:01
發布數100
最新版本名稱v1.15.0 (發布於 )
第一版名稱v0.1.0 (發布於 )
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