As described in https://stackoverflow.com/questions/25847035/what-are-signature-and-text-signature-used-for-in-python-3-4, https://bugs.python.org/issue20586, and https://stackoverflow.com/questions/50537407/add-a-signature-with-annotations-to-extension-methods,  it is possible to embed a signature in docstrings for C functions, so that `help` and `inspect.signature` work properly on them. However, this functionality isn't documented anywhere. I think something should be added to the "extending and embedding the Python interpreter" tutorial.