circuitpython/README.rst

CircuitPython
=============

.. image:: https://s3.amazonaws.com/adafruit-circuit-python/CircuitPython_Repo_header_logo.png

|Build Status| |Doc Status| |License| |Discord| |Weblate|

`circuitpython.org <https://circuitpython.org>`__ \| `Get CircuitPython <#get-circuitpython>`__ \|
`Documentation <#documentation>`__ \| `Contributing <#contributing>`__ \|
`Branding <#branding>`__ \| `Differences from Micropython <#differences-from-micropython>`__ \|
`Project Structure <#project-structure>`__

**CircuitPython** is a *beginner friendly*, open source version of Python for tiny, inexpensive
computers called microcontrollers. Microcontrollers are the brains of many electronics including a
wide variety of development boards used to build hobby projects and prototypes. CircuitPython in
electronics is one of the best ways to learn to code because it connects code to reality. Simply
install CircuitPython on a supported USB board usually via drag and drop and then edit a ``code.py``
file on the CIRCUITPY drive. The code will automatically reload. No software installs are needed
besides a text editor (we recommend `Mu <https://codewith.mu/>`_ for beginners.)

Starting with CircuitPython 7.0.0, some boards may only be connectable over Bluetooth Low Energy
(BLE). Those boards provide serial and file access over BLE instead of USB using open protocols.
(Some boards may use both USB and BLE.) BLE access can be done from a variety of apps including
`code.circuitpython.org <https://code.circuitpython.org>`_.

CircuitPython features unified Python core APIs and a growing list of 300+ device libraries and
drivers that work with it. These libraries also work on single board computers with regular
Python via the `Adafruit Blinka Library <https://github.com/adafruit/Adafruit_Blinka>`_.

CircuitPython is based on `MicroPython <https://micropython.org>`_. See
`below <#differences-from-micropython>`_ for differences. Most, but not all, CircuitPython
development is sponsored by `Adafruit <https://adafruit.com>`_ and is available on their educational
development boards. Please support both MicroPython and Adafruit.

Get CircuitPython
------------------

Official binaries for all supported boards are available through
`circuitpython.org/downloads <https://circuitpython.org/downloads>`_. The site includes stable, unstable and
continuous builds. Full release notes are available through
`GitHub releases <https://github.com/adafruit/circuitpython/releases>`_ as well.

Documentation
-------------

Guides and videos are available through the `Adafruit Learning
System <https://learn.adafruit.com/>`__ under the `CircuitPython
category <https://learn.adafruit.com/category/circuitpython>`__. An API
reference is also available on `Read the Docs
<http://circuitpython.readthedocs.io/en/latest/?>`__. A collection of awesome
resources can be found at `Awesome CircuitPython <https://github.com/adafruit/awesome-circuitpython>`__.

Specifically useful documentation when starting out:

- `Welcome to CircuitPython <https://learn.adafruit.com/welcome-to-circuitpython>`__
- `CircuitPython Essentials <https://learn.adafruit.com/circuitpython-essentials>`__
- `Example Code <https://github.com/adafruit/Adafruit_Learning_System_Guides/tree/master/CircuitPython_Essentials>`__

Code Search
------------
GitHub doesn't currently support code search on forks. Therefore, CircuitPython doesn't have code search through GitHub because it is a fork of MicroPython. Luckily, `SourceGraph <https://sourcegraph.com/github.com/adafruit/circuitpython>`_ has free code search for public repos like CircuitPython. So, visit `sourcegraph.com/github.com/adafruit/circuitpython <https://sourcegraph.com/github.com/adafruit/circuitpython>`_ to search the CircuitPython codebase online.

Contributing
------------

See
`CONTRIBUTING.md <https://github.com/adafruit/circuitpython/blob/main/CONTRIBUTING.md>`__
for full guidelines but please be aware that by contributing to this
project you are agreeing to the `Code of
Conduct <https://github.com/adafruit/circuitpython/blob/main/CODE_OF_CONDUCT.md>`__.
Contributors who follow the `Code of
Conduct <https://github.com/adafruit/circuitpython/blob/main/CODE_OF_CONDUCT.md>`__
are welcome to submit pull requests and they will be promptly reviewed
by project admins. Please join the
`Discord <https://adafru.it/discord>`__ too.

Branding
------------

While we are happy to see CircuitPython forked and modified, we'd appreciate it if forked releases
not use the name "CircuitPython" or the Blinka logo. "CircuitPython" means something special to
us and those who learn about it. As a result, we'd like to make sure products referring to it meet a
common set of requirements.

If you'd like to use the term "CircuitPython" and Blinka for your product here is what we ask:

- Your product is supported by the primary
  `"adafruit/circuitpython" <https://github.com/adafruit/circuitpython>`_ repo. This way we can
  update any custom code as we update the CircuitPython internals.
- Your product is listed on `circuitpython.org <https://circuitpython.org>`__ (source
  `here <https://github.com/adafruit/circuitpython-org/>`_). This is to ensure that a user of your
  product can always download the latest version of CircuitPython from the standard place.
- Your product supports at least one standard "`Workflow <https://docs.circuitpython.org/en/latest/docs/workflows.html>`__" for serial and file access:

  - With a user accessible USB plug which appears as a CIRCUITPY drive when plugged in.
  - With file and serial access over Bluetooth Low Energy using the BLE Workflow.
  - With file access over WiFi using the WiFi Workflow with serial access over USB and/or WebSocket.

- Boards that do not support the USB Workflow should be clearly marked.

If you choose not to meet these requirements, then we ask you call your version of CircuitPython
something else (for example, SuperDuperPython) and not use the Blinka logo. You can say it is
"CircuitPython-compatible" if most CircuitPython drivers will work with it.

--------------

Differences from `MicroPython <https://github.com/micropython/micropython>`__
-----------------------------------------------------------------------------

CircuitPython:

-  Supports native USB on most boards and BLE otherwise, allowing file editing without special tools.
-  Floats (aka decimals) are enabled for all builds.
-  Error messages are translated into 10+ languages.
-  Concurrency within Python is not well supported. Interrupts and threading are disabled.
   async/await keywords are available on some boards for cooperative multitasking. Some concurrency
   is achieved with native modules for tasks that require it such as audio file playback.

Behavior
~~~~~~~~

-  The order that files are run and the state that is shared between
   them. CircuitPython's goal is to clarify the role of each file and
   make each file independent from each other.

   -  ``boot.py`` runs only once on start up before
      workflows are 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``.
   -  ``code.py`` (or ``main.py``) is run after every reload until it
      finishes or is interrupted. After it is done running, the vm and
      hardware is reinitialized. **This means you cannot read state from**
      ``code.py`` **in the REPL anymore, as the REPL is a fresh vm.** CircuitPython's goal for this
      change includes reducing confusion about pins and memory being used.
   -  After the main code is finished the REPL can be entered by pressing any key.
      - If the file ``repl.py`` exists, it is executed before the REPL Prompt is shown
      - In safe mode this functionality is disabled, to ensure the REPL Prompt can always be reached
   -  Autoreload state will be maintained across reload.

-  Adds a safe mode that does not run user code after a hard crash or brown out. This makes it
   possible to fix code that causes nasty crashes by making it available through mass storage after
   the crash. A reset (the button) is needed after it's fixed to get back into normal mode.
-  Safe mode may be handled programmatically by providing a ``safemode.py``.
   ``safemode.py`` is run if the board has reset due to entering safe mode, unless the safe mode
   initiated by the user by pressing button(s).
   USB is not available so nothing can be printed.
   ``safemode.py`` can determine why the safe mode occurred
   using ``supervisor.runtime.safe_mode_reason``, and take appropriate action. For instance,
   if a hard crash occurred, ``safemode.py`` may do a ``microcontroller.reset()``
   to automatically restart despite the crash.
   If the battery is low, but is being charged, ``safemode.py`` may put the board in deep sleep
   for a while. Or it may simply reset, and have ``code.py`` check the voltage and do the sleep.
-  RGB status LED indicating CircuitPython state.
   - One green flash - code completed without error.
   - Two red flashes - code ended due to an exception.
   - Three yellow flashes - safe mode. May be due to CircuitPython internal error.
-  Re-runs ``code.py`` or other main file after file system writes by a workflow. (Disable with
   ``supervisor.disable_autoreload()``)
-  Autoreload is disabled while the REPL is active.
-  ``code.py`` may also be named ``code.txt``, ``main.py``, or ``main.txt``.
-  ``boot.py`` may also be named ``boot.txt``.
-  ``safemode.py`` may also be named ``safemode.txt``.

API
~~~

-  Unified hardware APIs. Documented on
   `ReadTheDocs <https://circuitpython.readthedocs.io/en/latest/shared-bindings/index.html>`_.
-  API docs are Python stubs within the C files in ``shared-bindings``.
-  No ``machine`` API.

Modules
~~~~~~~

-  No module aliasing. (``uos`` and ``utime`` are not available as
   ``os`` and ``time`` respectively.) Instead ``os``, ``time``, and
   ``random`` are CPython compatible.
-  New ``storage`` module which manages file system mounts.
   (Functionality from ``uos`` in MicroPython.)
-  Modules with a CPython counterpart, such as ``time``, ``os`` and
   ``random``, are strict
   `subsets <https://circuitpython.readthedocs.io/en/latest/shared-bindings/time/__init__.html>`__
   of their `CPython
   version <https://docs.python.org/3.4/library/time.html?highlight=time#module-time>`__.
   Therefore, code from CircuitPython is runnable on CPython but not
   necessarily the reverse.
-  tick count is available as
   `time.monotonic() <https://circuitpython.readthedocs.io/en/latest/shared-bindings/time/__init__.html#time.monotonic>`__

--------------

Project Structure
-----------------

Here is an overview of the top-level source code directories.

Core
~~~~

The core code of
`MicroPython <https://github.com/micropython/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 CircuitPython 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 pyboard.py module.

Ports
~~~~~

Ports include the code unique to a microcontroller line.

================  ============================================================
Supported         Support status
================  ============================================================
atmel-samd        ``SAMD21`` stable | ``SAMD51`` stable
cxd56             stable
espressif         ``ESP32`` beta | ``ESP32-C3`` beta | ``ESP32-S2`` stable | ``ESP32-S3`` beta
litex             alpha
mimxrt10xx        alpha
nrf               stable
raspberrypi       stable
silabs (efr32)    alpha
stm               ``F4`` stable | ``others`` beta
unix              alpha
================  ============================================================

-  ``stable`` Highly unlikely to have bugs or missing functionality.
-  ``beta``   Being actively improved but may be missing functionality and have bugs.
-  ``alpha``  Will have bugs and missing functionality.

Boards
~~~~~~

-  Each ``port`` has a ``boards`` directory containing boards
   which belong to a specific microcontroller line.
-  A list of native modules supported by a particular board can be found
   `here <https://circuitpython.readthedocs.io/en/latest/shared-bindings/support_matrix.html>`__.

`Back to Top <#circuitpython>`__

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