If you want to use the MU editor with the BirdBrain Technologies Python library automatically loading on MacOS, you first need to download the BirdBrain-Python-Library from either:

https://www.birdbraintechnologies.com/hummingbirdbit/python/install/2-2

or directly from the original github source at:

https://github.com/BirdBrainTechnologies/BirdBrain-Python-Library

In you will find a file BirdBrain.py which contains the entire python library.

When the MU editor loads, it can find python library files in this directory (the name will vary depending on the version of python):

/Applications/Mu Editor.app/Contents/Resources/Python/lib/python3.7

You can copy the BirdBrain.py file into this directory and restart the MU editor.

Update 2022.02.28: The location for mu version 1.1.1 is /Applications/Mu Editor.app/Contents/Resources/Python/lib/python3.8.

As an alternative, you can create a symbolic link to the file somewhere else on your system. For example, on my system, I have all github repositories in /Users/fmorton/GitHub. So, if the BirdBrain-Python-Library is in the GitHub directory, you can create the symbolic link by doing the following (the quotes are required in the first line because of the space in the "Mu Editor.app" directory name:

cd '/Applications/Mu Editor.app/Contents/Resources/Python/lib/python3.7'
ln -s /Users/fmorton/GitHub/BirdBrain-Python-Library/BirdBrain.py

After this, if you restart the MU editor, the BirdBrain library will be available for all running python code when using the editor.

Select the "Mode" button in the upper-left corner of the main navigation and select "Python 3".