def get_generic_bases(tp):
return getattr(tp, '<STR_LIT>', ())<EOL>
Get generic base types of a type or empty tuple if not possible.
    Example::

        class MyClass(List[int], Mapping[str, List[int]]):
            ...
        MyClass.__bases__ == (List, Mapping)
        get_generic_bases(MyClass) == (List[int], Mapping[str, List[int]])