Adafruit CircuitPython

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This is an open source derivative of MicroPython for use on educational development boards designed and sold by Adafruit.

As a MicroPython derivative, this implements Python 3.x on microcontrollers such as the SAMD21 and ESP8266.

Project Status

This project is in beta. Most APIs should be stable going forward.


Official binaries are available through the latest GitHub releases. Continuous (one per commit) builds are available here which includes experimental hardware support.


Guides and videos are available through the Adafruit Learning System under the CircuitPython category and MicroPython category. An API reference is also available on Read the Docs.


See for full guidelines but please be aware that by contributing to this project you are agreeing to the Code of Conduct. Contributors who follow the Code of Conduct are welcome to submit pull requests and they will be promptly reviewed by project admins. Please join the Gitter chat too.

Differences from MicroPython

  • Port for Atmel SAMD21 (Commonly known as M0 in product names.)
  • No machine API on Atmel SAMD21 port.
  • Only supports Atmel SAMD21 and ESP8266 ports.
  • The order that files are run and the state thats shared between them. The goal is to clarify the role of each file and make them independent from each other.
    • (or runs only once on start up before USB is initialized. This lays the ground work for configuring USB at startup rather than it being fixed. Since serial is not available, output is written to boot_out.txt.
    • (or is run after every reload until it finishes or is interrupted. After its done the vm and hardware is reinitialized. This means you cannot read state from in the REPL anymore. This was changed to reduce confusion about pins and memory being in use.
    • After the REPL can be entered by pressing any key. It no longer shares state with so its a fresh vm.
    • Autoreload state will be maintained across reload.
  • Adds a safe mode that does not run user code after a hard crash or brown out. The hope is that this will make it easier to fix code that causes nasty crashes by making it available through mass storage after the crash. A reset (the button) is needed after its fixed to get back into normal mode.
  • Unified hardware APIs: audioio, analogio, busio, digitalio, pulseio, touchio, microcontroller, board, bitbangio (Only available on atmel-samd21 and ESP8266 currently.)
  • Tracks MicroPython’s releases (not master).
  • No module aliasing. (uos and utime are not available as os and time respectively.)
  • Modules with a CPython counterpart, such as time, are strict subsets of their CPython version. Therefore, code from CircuitPython is runnable on CPython but not necessarily the reverse.
  • tick count is available as time.monotonic()
  • os only available as uos
  • atmel-samd21 features
    • RGB status LED
    • Auto-reload after file write over mass storage. (Disable with samd.disable_autoreload())
    • Wait state after boot and main run, before REPL.
    • Main is one of these: code.txt,,, main.txt
    • Boot is one of these: settings.txt,,, boot.txt

Project Structure

Here is an overview of the top-level directories.


The core code of MicroPython is shared amongst ports including CircuitPython:

  • docs High level user documentation in Sphinx reStructuredText format.
  • drivers External device drivers written in Python.
  • examples A few example Python scripts.
  • extmod Shared C code used in multiple ports’ modules.
  • lib Shared core C code including externally developed libraries such as FATFS.
  • logo The MicroPython logo.
  • mpy-cross A cross compiler that converts Python files to byte code prior to being run in MicroPython. Useful for reducing library size.
  • py Core Python implementation, including compiler, runtime, and core library.
  • shared-bindings Shared definition of Python modules, their docs and backing C APIs. Ports must implement the C API to support the corresponding module.
  • shared-module Shared implementation of Python modules that may be based on common-hal.
  • tests Test framework and test scripts.
  • tools Various tools, including the module.


Ports include the code unique to a microcontroller line and also variations based on the board.

  • atmel-samd Support for SAMD21 based boards such as Arduino Zero, Adafruit Feather M0 Basic, and Adafruit Feather M0 Bluefruit LE.
  • bare-arm A bare minimum version of MicroPython for ARM MCUs.
  • cc3200 Support for boards based CC3200 from TI such as the WiPy 1.0.
  • esp8266 Support for boards based on ESP8266 WiFi modules such as the Adafruit Feather HUZZAH.
  • minimal A minimal MicroPython port. Start with this if you want to port MicroPython to another microcontroller.
  • pic16bit Support for 16-bit PIC microcontrollers.
  • qemu-arm Support for ARM emulation through QEMU.
  • stmhal Support for boards based on STM32 microcontrollers including the MicroPython flagship PyBoard.
  • teensy Support for the Teensy line of boards such as the Teensy 3.1.
  • unix Support for UNIX.
  • windows Support for Windows.
  • zephyr Support for Zephyr, a real-time operating system by the Linux Foundation.

CircuitPython only maintains the atmel-samd and esp8266 ports. The rest are here to maintain compatibility with the MicroPython parent project.