Play with Python to learn it better.
https://codehabitude.com/2013/12/24/python-objects-mutable-vs-immutable/
https://www.youtube.com/watch?v=DEwgZNC-KyE
See unit tests for expected behavior. Tests aren't to check Python's implementation, but check my understanding.
python3 -m unittest discover -s tests/
set configuration "unit tests"