creating a subclassable extension type - need example

[Paul Miller]

I am trying to make an extension type that can be subclassed with Python
code, using the new 2.2.2 type system. I have used the fileobject.c Type
definition as an example, but do not know how to get a Python type to
actually subclass from it.

Is there a recent example of how to create a properly-subclassable C
extension type? Something I can define base methods in, and allow them to
be overriden by a Python subclass - then I intend to call the methods from
within C, and (hopefully) get the subclassed method behavior.

Thanks!