code: def off(self, event):
          'Remove an event handler'
          try:
              self._once_events.remove(event)
          except KeyError:
              pass
          self._callback_by_event.pop(event, Nonef off(self, event):
          'Remove an event handler'
          try:
              self._once_events.remove(event)
          except KeyError:
              pass
          self._callback_by_event.pop(event, None)
docs: Remove an event handler