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CircuitPython 4.0.1 released!

4.0.1 is our first bugfix release of 4.x and features fixes for two bugs. Download it now from See here for the full release notes.

4.0.0 features a port to the Nordic nRF52840 microcontroller, including support as a BLE beacon or peripheral (bleio), extensive new support for pixel-based displays (displayio) (guide here), which will show CircuitPython output on the display, USB MIDI support and messages translated into multiple languages. Current languages are Chinese (Pinyin), English, French, German, Indonesian, Italian, Polish, Spanish, and Tagalog (Filipino). Thank you to the many contributors who make CircuitPython excellent!

Over 50 boards are now supported by CircuitPython 4.0.1. Check out the new page for full list of all available versions.

It’s not too late to contribute to CircuitPython! Check out this guide for details. We’re always looking to improve and expect many stable releases in the 4.x line to happen through the summer. Subscribe to the Python for Microcontrollers newsletter on for the latest news for all things Python.
Downloads are now available from! This site makes it much easier to select the correct file and language for your board. The downloads page is here.

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).

New Fixes since 4.0.0
The stage library has been updated to 1.0.2 to fix a new OverflowError with read_palette introduced in 4.0.0-rc.3. Thanks to @deshipu
Enable round() which was enabled in 3.1.2. Thanks to @dhalbert
Breaking Changes from 3.x!
ESP8266 is no longer supported. With 4.x we’ve chosen to focus on microcontrollers with built-in USB to ensure a consistent CircuitPython experience across all boards we support.
ure, ujson, and uerrno renamed to re, json, and errno to reflect that they are subsets of the CPython library modules. Thanks to @dhalbert.
busio.UART breaking changes to match PySerial. Thanks to @dhalbert.
busio.UART constructor timeout parameter is now in seconds instead of milliseconds.
UART.readinto(buf) now does not allow an optional length parameter UART.readinto(buf, len).
UART.write(…) no longer allows strings to be written. The bytes written must be bytes or bytearray or an array.array.
framebuf has been removed. displayio is its replacement, and will be enhanced after 4.0 to include framebuf‘s functionality. Thanks to @tannewt.
Improve struct compatibility with CPython by enforcing stricter types. This may break your code! Thanks to @dhalbert.
bytearray, array.array, and int.to_bytes() now check for values that are too large to fit. This matches CPython behavior. Thanks to @godlygeek.”

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