I think that we should re-examine this issue after GH-20472 is merged. I'm not really sure how that will affect this and indeed *how* it should affect this. I am not sure whether people are relying on the current behavior, or what use cases would be improved if we had a different behavior.

With regards to this:

> The documentation for getfile says "This will fail with a TypeError if the object is a built-in module, class, or function."

> https://docs.python.org/3/library/inspect.html#inspect.getfile

This is a bit unclear to me, and I'm not entirely sure if `datetime` qualifies. I think of built-in classes as things like `int` and `float`, and built-in functions as things like `abs` and `sum`, and `datetime` is an extension module — albeit one with a C implementation, and one that is in the standard library.

We should probably clarify the wording of `inspect.getsource` and determine what the intended semantics are for PEP-399-style modules, with both a C and pure Python implementation and the C implementation is what's being used. Error? Point to the Python implementation?