Example of a Python 3 inner class as a C/C++ extension

Example of a Python 3 inner class as a C/C++ extension

I would like to create a python 3 extension to allow me to write something
like the following:
ClassA.ClassB.some_class_method_of_B()
Both ClassA and ClassB are (will be) defined as Python 3 extensions in
C/C++. I've written python extensions before, so I know the basics, but I
can't find an example of creating inner classes. Is there an example in
python's source code that I could take a look at ?
Thanks.