code: def clear(self):
          
          self.services.clear()
          self._future_value.clear()
  
          self.services = None
          self._lock = None
          self._ipopo_instance = None
          self._context = None
          self.requirement = None
          self._key = None
          self._allow_none = None
          self._future_value = None
          self._field = None
docs: Cleans up the manager. The manager can't be used after this method has
          been called