def get_Mapping_key_value(mp):
    """Retrieves the key and value types from a PEP 484 mapping or subclass of such.
    mp must be a (subclass of) typing.Mapping.
    """
    try:
        res = _select_Generic_superclass_parameters(mp, typing.Mapping)
    except TypeError:
        res = None
    if res is None:
        raise TypeError("Has no key/value types: "+type_str(mp))
    else:
        return tuple(res)
Retrieves the key and value types from a PEP 484 mapping or subclass of such.
    mp must be a (subclass of) typing.Mapping.