code: def fixup_namespace_packages(path_item, parent=None):
      
      _imp.acquire_lock()
      try:
          for package in _namespace_packages.get(parent, ()):
              subpath = _handle_ns(package, path_item)
              if subpath:
                  fixup_namespace_packages(subpath, package)
      finally:
          _imp.release_lock()
docs: Ensure that previously-declared namespace packages include path_item