Add docstrings to Python code

[mihaic]

They are very helpful for interactive use.

You can also use them to generate HTML documentation automatically with sphinx-apidoc: http://www.sphinx-doc.org/en/stable/man/sphinx-apidoc.html

[ifadams]

While this is a reasonable ask, we should consider it more as an ongoing maintenance task/revisit given age of ticket. Closing for now. @cwlacewe