Do you mean Python addons? There are no strict rules, but following general Python best practices is strongly recommended.
PEP-8 is the official coding style guide for Python.
As for docstrings, docstring with reStructuredText formatting and
Sphinx directives are the
de facto standard in Python world. PyCharm IDE can even use Sphinx directives for function/method parameters/returns as type hints for static code analysis (proper type hints have been added only in Python 3.5), highlighting potential issues with type mismatch.