Jumping in here to explain why '__class' doesn't crash when '__sizeof__' does:

When '__class__' is fetched, it returns a new reference to the object's type.

When '__sizeof__' is fetched on the otherhand, a new object is allocated on the heap ('types.MethodType') and is returned to the caller.

This object also has a '__sizeof__' that does the same (as it's implemented on 'object'.

So yes, you are exhausting the C runtime stack by de-allocating over a THOUSAND objects.

You can see this happen by watching the memory usage of Python steadily climb.