Mu’s Architecture

This section provides a high level overview of how the various parts of Mu fit together.

Key Concepts

The key concepts you should know are:

  • Mu uses the PyQT5 framework (that makes the Qt GUI toolkit available to Python) for making its user interface.

  • Mu is a modal editor: the behaviour of Mu changes, depending on mode.

  • There are a number of core features and behaviours that are always available and never vary, no matter the mode.

  • The text area into which users type code is based on a Scintilla based widget.

  • Mu is easy to internationalise using Python’s standard gettext based modules and tools.

  • Mu’s code base is small, well documented and has 100% unit test coverage.

Code Structure

The code is found in the mu directory and organised in the following way:

  • The application is created and configured in

  • Most of the fundamental logic for Mu is in

  • Un-packaged third party code used by Mu is found in contrib.

  • The Python3 debugger consists of a debug client and debug runner found in the debugger namespace. A description of how the debugger works can be found in Python Runner/Debugger.

  • Interacting with the UI layer is done via the Window class in the interface.main module. Mu specific UI code used by the Window class found in the other modules in the namespace.

  • Internationalization (I18n) related assets are found under locale. Learn how this works via Internationalisation of Mu.

  • Modes are found under the modes namespace. They all inherit from a BaseMode class and there’s a tutorial for Modes in Mu.

  • Graphical assets, fonts and CSS descriptions for the themes are all found under resources.

All classes, methods and functions have documentation written for humans. These are extracted into the Mu API Reference.

Mu’s Test Suite is in the test directory and filenames for tests relate directly to the file they test in the Mu code base. The module / directory structure mirrors the organisation of the Mu code base. We use PyTest’s assert based unit testing. All tests have a comment describing their intent.

The documentation you’re reading right now (i.e. that written for developers) is found in the docs directory. We use Sphinx to write our docs and host them on ReadTheDocs. Other documentation (tutorials, user help and so on) is on Developing Mu’s Website.

The utils directory contains various scripts used to scrape and / or build the API documentation used by Mu’s autocomplete and call tip functionality.

The other assets in the root directory of the project are mainly for documentation (such as our Code of Conduct), configuration (for testing) or packaging for various platforms (see Packaging Mu).

If you want to make changes please read Contributing to Mu.