Mypy is a Python variant with seamless dynamic and static typing. Currently the mypy implementation lets you mix static types and dynamic types and translate mypy programs to readable Python. Type annotations and casts are treated as comments when translating to Python.
The main goal of the project is to develop an optimising compiler that can compile mypy programs to efficient native code. The compiler is still early in development.
Mypy is work in progress; many features are missing and there are still bugs. See 'Development status' below.
You need Python 3.x 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
For OS X, Windows and other Linux flavours, packages are available at
There is a separate repository that contains the mypy implementation translated to Python. You need to clone it to actually run mypy:
$ git clone https://github.com/JukkaL/mypy-py.git
Now you can run mypy programs:
$ python3 <path-to-repo>/mypy-py/driver.py PROGRAM
Replace 'python3' with your Python 3 interpreter.
The 'mypy-py' repository is only used for running mypy. For mypy development, clone the 'mypy' repository:
$ git clone https://github.com/JukkaL/mypy.git
Remember to keep the two repos in sync by pulling them both; otherwise you might get mysterious errors.
Documentation and additional information is available at the web site:
To run tests, run the script 'tests.py' in the 'mypy' repository using the 'mypy.py' driver. (We use the .py extension for mypy programs even though they are not typically valid Python. This is handy since syntax highlighting in editors etc. typically just works.)
Mypy is work in progress and is not yet production quality (though mypy development is already done in mypy!).
Here are some of the more significant Python features not supported right now (but all of these will improve):
- no decorators (neither properties)
- no 'with' statements
- no nested classes
- no metaclasses
- only basic operator overloading
- only some Python modules are supported, and some only partially
Some mypy-specific features are also not supported or only partially supported, including these:
- function overloading does not work properly in all cases, including some instances of method overriding
- no 'dynamic' classes
- there is no way to use dynamic typing by default for top-level code
The initial development focus is to support a useful subset of Python features. The next main task is to implement an efficient native compiler for this subset. Other features will be implemented as well, prioritized based on user feedback.
Please report any bugs and enhancement ideas using the mypy issue tracker:
https://github.com/JukkaL/mypy/issues
Any help in testing, development, documentation and other tasks is highly appreciated and useful to the project. Contact the developers to join the project, or just start coding and send pull requests! There are tasks for contributors of all skill levels.
Mypy is licensed under the terms of the MIT license (see the file LICENSE).