Type annotations in Python: The mypy static type-checker

The pieces of code stored here were initially written to present Type Annotations in Python and Static Type-Checking during the PhDCircus event organized on 2019, May 24 at TDB. The Jupyter/IPython Notebook mypy_examples.ipynb aimed to show live example of code run either with the mypy type checker or with the regular Python interpreter.

Getting Started

The repository contains, along the IPython code:

• mypy.ini: an example of configuration file for mypy,
• mytuples.py: a simple short piece of code for illustrating the use of mypy with Python (and not IPython),
• mypycheck.py: a piece of code for making mypy static type-checking usable with the IPython environment.

Prerequisites

Python >= 3.5, for example on Ubuntu systems (further info at https://realpython.com/installing-python/)

$ sudo apt-get update
$ sudo apt-get install python3.x

Jupyter Notebook (Formerly known as the IPython Notebook)

$ python3 -m pip install --upgrade pip
$ python3 -m pip install jupyter

The installation of Jupyter Notebook above will also install the IPython kernel which allows working on notebooks using the Python programming language.

Alternatively,

IPython (Productive Interactive Computing), provides a kernel for Jupyter

$ pip install ipython

mypy

$ pip install mypy

Installing

The installation of IPython should create a .ipython folder at your system's home folder.

The code for the customized magic function mypycheck.py has to be saved at

 ~/.ipython/profile_default/startup/mypycheck.py

Running the Jupyter Notebook

Once you have saved the files in a project folder, open a terminal and run

$ cd /path/to/project
$ jupyter notebook

This should open a new tab/window in your browser with a locally-hosted Jupyter server (http://localhost:8888/tree) and a list of the files you downloaded, including the mypy_examples.ipynb file. Open the that file.

The Jupyter Notebook is ready for running!

References/Further Documentation

• https://docs.python.org/3/reference/compound_stmts.html#function
• https://docs.python.org/3/glossary.html#term-function-annotation
• https://www.python.org/dev/peps/pep-3107/
• https://docs.python.org/3/library/typing.html
• https://mypy.readthedocs.io/en/latest/index.html
• https://realpython.com/python-type-checking
• https://switowski.com/python/ipython/2019/02/15/creating-magic-functions-part3.html

Authors

• Camille Clouard - Initial work