@classmethod
def empty(cls):
    """This is a class method which returns an empty type system."""
    x = cls(base_types=set(), template_types={}, refined_types={},
        humannames={}, type_aliases={}, cpp_types={}, numpy_types={},
        from_pytypes={}, cython_ctypes={}, cython_cytypes={},
        cython_pytypes={}, cython_cimports={}, cython_cyimports={},
        cython_pyimports={}, cython_functionnames={}, cython_classnames={},
        cython_c2py_conv={}, cython_py2c_conv={})
    del x.extra_types
    del x.dtypes
    del x.stlcontainers
    return x
