docs: def restore(self):
          """Restores the modules that the saver knows about into
          sys.modules.
          """
          try:
              for modname, mod in self._saved.items():
                  if mod is not None:
                      sys.modules[modname] = mod
                  else:
                      try:
                          del sys.modules[modname]
                      except KeyError:
                          pass
          finally:
              imp.release_lock()