code: def expunge(self, instance=None):
          '''Remove ``instance`` from this :class:`Session`. If ``instance``
  is not given, it removes all instances from this :class:`Session`.'''
          if instance is not None:
              sm = self._models.get(instance._meta)
              if sm:
                  return sm.expunge(instance)
          else:
              self._models.clear(f expunge(self, instance=None):
          '''Remove ``instance`` from this :class:`Session`. If ``instance``
  is not given, it removes all instances from this :class:`Session`.'''
          if instance is not None:
              sm = self._models.get(instance._meta)
              if sm:
                  return sm.expunge(instance)
          else:
              self._models.clear()
docs: Remove ``instance`` from this :class:`Session`. If ``instance``
  is not given, it removes all instances from this :class:`Session`.