Developer Setup

The source code is hosted on GitHub. Fork the repository with the following command:

git clone

Mu does not and never will use or support Python 2. You should use Python 3.5 or above.

Windows, OSX, Linux

On all platforms except the Raspberry Pi, to create a working development environment install all the dependencies into your virtualenv via the requirements.txt file:

pip install -r requirements.txt


Sometimes, having several different versions of PyQt installed on your machine can cause problems (see this issue for example).

Using a virtualenv will ensure your development environment is safely isolated from such problematic version conflicts.

If in doubt, throw away your virtualenv and start again with a fresh install from requirements.txt as per the instructions above.

On Windows, use the venv module from the standard library to avoid an issue with the Qt modules missing a DLL:

py -3 -mvenv .venv

Running Development Mu


From this point onwards, instructions assume that you’re using a virtual environment.

For the debug runner to work, the mu-debug command must be available (it’s used to launch user’s Python script with the debugging scaffolding in place to communicate with Mu, acting as the debug client). As a result, it’s essential to run the following to ensure this command is available in your virtualenv:

pip install --editable .

To run the local development version of Mu, in the root of the repository type:


An alternative form is to type:

python -m mu

Raspberry Pi

If you are working on a Raspberry Pi there are additional steps to create a working development environment:

  1. Install required dependencies from Raspbian repository:

    sudo apt-get install python3-pyqt5 python3-pyqt5.qsci python3-pyqt5.qtserialport python3-pyqt5.qtsvg python3-dev python3-gpiozero python3-pgzero libxmlsec1-dev libxml2 libxml2-dev
  2. Create a virtualenv that uses Python 3 and allows the virtualenv access to the packages installed on your system via the --system-site-packages flag:

    sudo pip3 install virtualenv
    virtualenv -p /usr/bin/python3 --system-site-packages ~/mu-venv
  3. Activate the virtual environment

    source ~/mu-venv/bin/activate
  4. Clone mu:

    (mu-venv) $ git clone ~/mu-source
  5. With the virtualenv enabled, pip install the Python packages for the Raspberry Pi via the requirements.txt file:

    (mu-venv) $ cd ~/mu-source
    (mu-venv) $ pip install -r requirements.txt
  1. Use pip to install mu without installing the dependencies again:

    (mu-venv) $ pip install --editable .
  2. Run mu:


    An alternative form is to type:

    python -m mu


These instructions for Raspberry Pi only work with Raspbian version “Stretch”.

If you use pip to install Mu on a Raspberry Pi, then the PyQt related packages will not be automatically installed from PyPI. This is why you need to use apt-get to install them instead, as described in step 1, above.

Using make

There is a Makefile that helps with most of the common workflows associated with development. Typing make on its own will list the options thus:

$ make

There is no default Makefile target right now. Try:

make run - run the local development version of Mu.
make clean - reset the project and remove auto-generated assets.
make pyflakes - run the PyFlakes code checker.
make pycodestyle - run the PEP8 style checker.
make test - run the test suite.
make coverage - view a report on test coverage.
make check - run all the checkers and tests.
make dist - make a dist/wheel for the project.
make publish-test - publish the project to PyPI test instance.
make publish-live - publish the project to PyPI production.
make docs - run sphinx to create project documentation.
make translate - create a messages.pot file for translations.
make translateall - as with translate but for all API strings.

Everything should be working if you can successfully run:

make check

(You’ll see the results from various code quality tools, the test suite and code coverage.)


On Windows there is a make.cmd file that works in a similar way to the make command on Unix-like operating systems.


In order to use the MicroPython REPL via USB serial you may need to add yourself to the dialout group on Linux, or, if you’re on some versions of Windows, install the Windows serial driver.

Before Submitting

Before contributing code please make sure you’ve read Contributing to Mu and follow the checklist for contributing changes. We expect everyone participating in the development of Mu to act in accordance with the PSF’s Code of Conduct.