<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _dispatch_legacy_subscriber(self, obj, *args, **kwargs):
 """This dispatches the registered callback for 'obj'. This is only used for legacy subscribers since new users should register with the target object directly."""

    if obj in self._legacy_subscribers:
      self._legacy_subscribers[obj](obj)