Method Name:
cancel
Method Signature:
cancel(event)
Parameters:
event – An event that has been already registered with a scheduler instance which needs to be cancelled.
Return Value:
None
Exceptions:
Raises a ValueError when the event is not found in the internal queue of a scheduler instance.
Overview:
- The cancel() method of the scheduler class from the Python Standard Library module sched, removes an already scheduled event from a scheduler instance.
- The cancel() method does not remove an event from the queue once the scheduler is started by calling the run() method.
Example:
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# Example Python program to cancel an already scheduler # event with a scheduler instance import sched import time
def eventFunction(description): print("Executing event:%s"%description);
# Create an event scheduler eventScheduer = sched.scheduler(time.time, time.sleep);
# Add events to the scheduler e1 = eventScheduer.enterabs(time.time()+5, 1, eventFunction, argument= ("Event1",)); e2 = eventScheduer.enterabs(time.time()+10, 1, eventFunction, argument= ("Event2",)); e3 = eventScheduer.enterabs(time.time()+15, 2, eventFunction, argument= ("Event3",));
# Remove an event before the scheduler starts eventScheduer.cancel(e1);
eventScheduer.run();
# Remove an event after the scheduler starts...which fails eventScheduer.cancel(e3); |
Output:
The example Python program removes the e1 from the queue. However, once the scheduler is started it is unable to remove e3.
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Executing event:Event2 Executing event:Event3 Traceback (most recent call last): File "cancelex.py", line 23, in <module> eventScheduer.cancel(e3); File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/sched.py", line 96, in cancel self._queue.remove(event) ValueError: list.remove(x): x not in list |