code: def UnregisterEventHandler(self, Event, Target):
          
          if not callable(Target):
              raise TypeError('%s is not callable' % repr(Target))
          if Event not in self._EventHandlers:
              raise ValueError('%s is not a valid %s event name' % (Event, self.__class__.__name__))
          if Target in self._EventHandlers[Event]:
              self._EventHandlers[Event].remove(Target)
              self.__Logger.info('unregistered %s: %s', Event, repr(Target))
              return True
          return False
docs: Unregisters an event handler previously registered with `RegisterEventHandler`.
  
          :Parameters:
            Event : str
              Name of the event. For event names, see the respective ``...Events`` class.
            Target : callable
              Callable to unregister.
  
          :return: True if callable was successfully unregistered, False if it wasn't registered
                   first.
          :rtype: bool
  
          :see: `RegisterEventHandler`