Had to recently document a Python library / API; it was not for public consumption. I took inspiration from pyserial [1] and made sparse docstrings which in turn reduced potential clutter making things easier to read and digest; and provide a more elaborate (hand generated) documentation in the sphinx documentation rendered as html/pdf. I quite liked this balance. The obvious trade off is the sphinx documentation may go out of sync with what is in the code, but eh if it happens it won't be the end of the world and is quickly rectified.
I would just say follow pyserial example if that is something you like; look at their source code docstrings vs the documentation including the API bits.
If that's something you like, then just lift their documentation/ wholesale and tailor it to your needs, which is how I started. I also tweaked the sphinx settings to generate a pdf as well, but that was a special thing for the customer we were delivering the library and documentation to.
[1]: https://pythonhosted.org/pyserial/