code: def unsubscribe(self, event, handler):
          
          try:
              self._handlers.sync_handlers[event].remove(handler)
          except ValueError:
              self._handlers.async_handlers[event].remove(handler)
          else:
              try:
                  self._handlers.async_handlers[event].remove(handler)
              except ValueError:
                  pass
docs: Unsubscribes the Handler from the given Event.
          Both synchronous and asynchronous handlers are removed.
  
          @param event: (str|see.Event) event to which the handler is subscribed.
          @param handler: (callable) function or method to unsubscribe.