CircuitPython 3.1.1 released! — @adafruit @CircuitPython

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Download the 3.1.1 release release from GitHub here:

Changes since 3.0.3

  • All frozen libraries have been updated to their latest versions as of 2018-11-01.
  • The default value of sys.path has been changed.
    ['', '/', '/lib', '.frozen']


    ['', '/', '.frozen', '/lib']

    This change causes the frozen library of a library to be found and loaded on import, instead of any non-frozen version in /lib. Previously, to make sure the frozen version of a library was used, you had to remove that library from /lib. Whenever you updated /lib with a new library bundle, this had to be repeated.

    When frozen libraries are imported they use up much less heap space (in RAM) than compiled .mpylibraries in /lib or elsewhere. This helps prevent running out of RAM when importing several modules or allocating large amounts of storage. This was a common support issue. Thanks to @kattni for advocating for this change, to @caternuson for discussion, and to @dhalbert for implementation.

    If you need to override a frozen library with a different version, simply place it in /, instead of in /lib. The version in / will be found first and will be used instead.

    Note that .frozen is not a real directory. It represents all the frozen modules. You cannot list it with os.listdir().

    The following builds include frozen libraries and are affected by this change: circuit_playground_express, circuit_playground_express_crickit, feather_m0_express_crickithallowing_m0_expresspirkey_m0.

Note: Release 3.1.0 is being skipped: the tag was created on the wrong commit. The tag has been deleted, but we’re skipping it to avoid confusion.


To install follow the instructions in our new Welcome to CircuitPython! guide. To install the latest libraries, see this page in that guide.

Try the latest version of the Mu editor for creating and editing your CircuitPython programs and for easy access to the CircuitPython serial connection (the REPL).

All builds are available as both UF2 and bin files here along with test builds.


Documentation is available on

Here are all the changes since 3.0.3.

This release is based on MicroPython 1.9.3. Support upstream MicroPython by purchasing a PyBoard (from Adafruit here).


Pre-built mpy-cross executables are available above for MacOS, Windows, Ubuntu, and Raspbian. For MacOS, Ubuntu, and Raspbian, you must make the mpy-cross download executable by doing. Then you can compile a .py file to .mpy:

$ chmod +x mpy-cross-whatever-you-downloaded         # you only need to do this once
$ ./mpy-cross-whatever-you-downloaded    # this will generate yourfile.mpy


Check out this guide for info on common problems with CircuitPython. If you are still having, then post to the Adafruit Support Forums and join Discord.

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