Types that are built into the Python interpreter.
PyO3 is designed in a way that all references to those types are bound to the GIL, which is why you can get a token from all references of those types.
unsafe fn unchecked_downcast(obj: &PyAny) -> &Self
&Self without no type checking.
obj must have the same layout as
*const ffi::PyObject and must be
an instance of a type corresponding to