Mu: A Python Code Editor



This documentation is NOT for users of Mu. Rather, it is for software developers who want to improve Mu. Read our Developer Setup documentation for the technical details needed to get started.

For tutorials, how-to guides and user related discussion, please see the project’s website for users of Mu at:

If you’re interested in the fun, educational, inspiring and sometimes hilarious ways in which people use Mu, check out:


Mu works with Python 3.5 to 3.8 (both inclusive). You need to have one of these Python versions installed in order to work on developing Mu (here is a comprehensive guide for how to do this). We also assume you know how to use Python virtual environments.

Clone the repository:

git clone

Create a virtualenv in Python 3.8:

python3.8 -m venv .venv

Activate the environment, on macOS and Linux the command is:

source .venv/bin/activate

For Windows, the command is:

. .\.venv\Scripts\activate.ps1

Once your virtual environment is activated, upgrade pip:

python -m pip install --upgrade pip

Install Mu and its development dependencies:

pip install -e ".[dev]"

Start Mu:


Run the test suite:

make check

Read on to learn more about Mu, its aims and how you can contribute.


Mu is a very simple Python editor for kids, teachers and beginner programmers. It’s written in Python and works on Windows, OSX, Linux and Raspberry Pi.

“[Papert] realized, ‘Oh, we could take the real content out here as a version in the child’s world that is still the real thing.’ It’s not a fake version of math. It’s kind of like little league, or even T-ball. In sports they do this all the time. In music, they do it all the time. The idea is, you never let the child do something that isn’t the real thing – but you have to work your ass off to figure out what the real thing is in the context of the way their minds are working at that developmental level.” – Alan Kay

Mu aspires to be “the real thing” as a development environment for beginner programmers taking their first steps with Python.

As a rule of thumb, if you’re able to ask “why doesn’t Mu have [feature X]?” then you’re probably too advanced for using Mu as a development environment. In which case, you should graduate to a more advanced editor.


There isn’t a cross platform Python code editor that is:

  • Easy to use;

  • Available on all major platforms;

  • Well documented (even for beginners);

  • Simply coded;

  • Currently maintained; and,

  • Thoroughly tested.

Mu addresses these needs.

Mu was originally created as a contribution from the Python Software Foundation for the BBC’s micro:bit project. Many people asked if Mu could be turned into a generic beginner’s code editor and, thanks to the wonderful support of the Raspberry Pi Foundation the work needed to make such changes was done over the summer of 2017.

The following video of a talk given at PyCon 2018 outlines the story of Mu:


Mu’s outlook is:

  • Less is more (remove all unnecessary distractions);

  • Keep it simple (so Mu is easy to understand);

  • Walk the path of least resistance (Mu should be easy to use);

  • Have fun (learning should be a positive experience).

Mu’s own code is simple, clearly organised and well tested. It’s copiously commented and mostly found in a few obviously named Python files.

This has been done on purpose: we want teachers and kids to take ownership of this project and organising the code in this way aids the first steps required to get involved.

If you’re looking for ways to get involved check out some of the Suggested First Steps for new contributors.

Furthermore, we put our users at the centre of our development work. Extensive interviews with teachers, observations of lessons and exceptionally clear and helpful feedback from the education team at the Raspberry Pi Foundation (perhaps the most successful computing in education project in history) have informed the design choices for Mu.



Contributions are welcome without prejudice from anyone irrespective of age, gender, religion, race or sexuality. If you’re thinking, “but they don’t mean me”, then we especially mean YOU. Good quality code and engagement with respect, humour and intelligence wins every time.

Read about Contributing to Mu and perhaps try out some Suggested First Steps.

We want the Mu community to be a friendly place. Therefore, we expect contributors to follow our Code of Conduct.