twisted.internet.defer.Deferred.cancel(self) method documentation

Cancel this Deferred.

If the Deferred has not yet had its errback or callback method invoked, call the canceller function provided to the constructor. If that function does not invoke callback or errback, or if no canceller function was provided, errback with CancelledError.

If this Deferred is waiting on another Deferred, forward the cancellation to the other Deferred.