MicroPython

MicroPython is a reimplementation of Python 3 that can be used with the BBC micro:bit

Overview

MicroPython is a version of the popular Python programming language for devices like the micro:bit. It’s free software: creating, maintaining and documenting MicroPython is the work of an international team of volunteers.

There are many ways to use MicroPython on the micro:bit. You can use:

The browser based Python Editor.
The offline Mu editor
Your regular editor to create Python files and a suite of command line tools to interact with the device (for advanced users only).
One of the third party editors listed on the website.

MicroPython Tools

uFlash A utility for flashing the BBC micro:bit with Python scripts and the MicroPython runtime. You pronounce the name of this utility “micro-flash”. ;-)

It provides two services: - A library of functions to programmatically create a hex file and flash it onto a BBC micro:bit. - A command line utility called uflash that will flash Python scripts onto a BBC micro:bit.

microFS A simple command line tool and module for interacting with the limited file system provided by MicroPython on the BBC micro:bit.

Finally, there are great tutorials for MicroPython on the micro:bit.

What is MicroPython?

MicroPython is just as easy to learn as the other programming languages but differs from them in several important respects:

MicroPython is a complete reimplementation of Python 3. This includes advanced features not found in any of the other languages: basic data types (strings, integers, floating point numbers, booleans), data structures (lists, dictionaries, sets), classes, exception handling, generators and list comprehensions.
MicroPython runs entirely on the micro:bit itself - no need for a compiler.
MicroPython (like Python) is a dynamic language so it’s possible to work with the device interactively: enter Python code and see the device immediately respond in live coding sessions using the REPL feature.
MicroPython comes with lots of exclusive features: a powerful music programming language, a speech synthesiser, built-in images and music, a local file system and a large range of ways to connect to attached devices: I2C, NeoPixel, SPI and UART.

V1 The Bluetooth stack is not enabled inside MicroPython because of memory constraints. However MicroPython uses the Bluetooth radio hardware with its own simple yet powerful radio module. The protocol for the radio module is a lot more beginner friendly than Bluetooth yet allows users to create efficient yet effective wireless networks of micro:bit devices. Conceptually it works in the same way as walkie-talkies: anyone broadcasting on a certain channel can be heard by anyone listening on the same channel (and there are a large selection of channels to tune into). That’s it!

Finally, and perhaps most importantly, by learning MicroPython you’re learning how to use Python - one of the world’s most popular professional programming languages. You inadvertently use Python every day when you use YouTube, Google, Facebook, Instagram, DropBox and a plethora of other online services. These skills are valuable: Python programmers are in demand.

The MicroPython Software

MicroPython is itself written in C++. The MicroPython “runtime” is built using a set of offline tools. The output from this build process is a .hex file containing the complete MicroPython language. The editors described above combine this file with your code to generate the file you copy onto the device.

You can flash just the runtime .hex file onto any micro:bit by simply making sure the editor based code is empty.

When MicroPython is loaded to the micro:bit in this way, it obviously doesn’t have a user program associated with it. But, you can connect to your micro:bit over the USB Serial port using a terminal program (or inside the Mu editor press the REPL button to do the same). You can then have a live conversation with MicroPython; for example if you type display.show("Hello"), the moment that you press RETURN the message "hello" will scroll on the screen.

More interesting still, if the .hex file you copied onto the device does contain some of your code, it’s still possible to connect with the REPL and interact with your program. This is very useful for debugging purposes.

Adding a User Application to MicroPython

Both the web hosted and the offline editor (Mu) have a copy of this MicroPython .hex file inside them, as a plain text file.

When you write your Python application, both the web hosted editor and the offline editor Mu create a modified .hex file for you to copy to the micro:bit. This modified file contains 3 things

An identical copy of the base MicroPython .hex code file;
A small header which marks a region as a MicroPython script (followed by the length of the script in bytes);
A verbatim copy of your Python program, complete with comments and any spaces.

As a result, Mu and the uflash command are able to retrieve your Python code from .hex files (even if you forgot to save your source code).

When you flash (i.e. copy) a .hex file into the micro:bit it reboots. MicroPython looks for your script in a special memory address. If it finds a script it’ll attempt to run it. Your program will run all the while there is something to do, so it will keep going all the while your program loops around, or until an error occurs (at which time the program will stop and scroll a helpful error message on the device).

Is MicroPython Compiled or Interpreted? It’s Both!

Compilation is when code is turned into instructions the computer understands. As a result, these instructions are evaluated very quickly. Interpretation is when code is run by another (interpreting) program instead of directly on the computer. Interpretation has the advantage of flexibility: it’s possible to interact with the interpreter while your program is running and change things. This is, in fact, what you’re doing when you live-code using the REPL. However, due to the interpretation process interpreted code is slower than compiled code.

MicroPython uses a combination of compilation and interpretation techniques to run your program. Here’s how:

When MicroPython sees a script it parses each line of the script. The end result is a set of in-memory tokens grouped in such a way that they represent how your program works. This is called the Abstract Syntax Tree (AST).

The AST is compiled into a terse set of instructions called Python bytecode. Bytecode instructions are like CPU assembly language instructions, but they are targeted for a virtual machine, not for a real piece of computer hardware.

The Python bytecode is given to the Python virtual machine to run and so your program is executed.

All of the above happens in the blink of an eye.

The Python virtual machine built into MicroPython is itself compiled from C++ code. It reads Python bytecodes and interprets them one at a time, calling into lower level C++ functions to make each one perform its unique purpose. By using a bytecode interpreter, MicroPython implements a virtual machine with its own virtual instruction set. It is virtual, because these instructions are not “baked in” to the hardware, but they are implemented in software. This is what allows MicroPython to be easily ‘ported’ onto different computer systems with different processors.

Code Editors and Tools

The Python in Education website contains lots of micro:bit related resources and an online editor as well as general Python in education related resources.

You can download Mu from its website and also get involved with its development. In addition, the browser based editor is open source and community maintained.

A couple of Python modules provide code and command line commands for flashing your micro:bit and interacting with the filesystem.

Community Contributions

Many people in the international Python community have contributed free-to-use resources via the MicroPython / BBC micro:bit World Tour.

Online python simulator

Teaching Resources

microbit.org Provides a range of Python related curricula.

NCCE key-stage 3 Physical computing Contains KS3 level curriculum for teaching Python with the micro:bit.

Grok Learning provides an online MicroPython code editor, Blockly visual programming, full micro:bit simulator, curriculum-aligned teaching material and auto-marked problems.

Documentation

Tutorials and API documentation for developers can be found here.