'Attempts to cancel a previously scheduled activity task. If
the activity task was scheduled but has not been assigned to a
worker, then it will be canceled. If the activity task was
already assigned to a worker, then the worker will be informed
that cancellation has been requested in the response to
RecordActivityTaskHeartbeat.'

def request_cancel_activity_task(self, activity_id):

    o = {}
    o['decisionType'] = 'RequestCancelActivityTask'
    attrs = o['requestCancelActivityTaskDecisionAttributes'] = {}
    attrs['activityId'] = activity_id
    self._data.append(o)
