def _module_matches_namespace(self, fullname):
        """Figure out if the target module is vendored."""
        root, base, target = fullname.partition(self.root_name + '.')
        return not root and any(map(target.startswith, self.vendored_names))
Figure out if the target module is vendored.
product/runtime/src/main/python/pkg_resources/extern/__init__.py