@classmethod
def find_spec(cls, fullname, path=None, target=None):
    '''
    前略...
    '''
    spec = cls._get_spec(fullname, path, target)
    if spec is None:
        return None
    elif spec.loader is None:
        namespace_path = spec.submodule_search_locations
        if namespace_path:
            # We found at least one namespace path.  Return a spec which
            # can create the namespace package.
            spec.origin = None
            spec.submodule_search_locations = _NamespacePath(fullname, namespace_path, cls._get_spec)
            return spec
        else:
            return None
    else:
        return spec