Source code: Lib/sched.py
sched module defines a class which implements a general purpose event
schedulerclass defines a generic interface to scheduling events. It needs two functions to actually deal with the “outside world” — timefunc should be callable without arguments, and return a number (the “time”, in any units whatsoever). The delayfunc function should be callable with one argument, compatible with the output of timefunc, and should delay that many time units. delayfunc will also be called with the argument
0after each event is run to allow other threads an opportunity to run in multi-threaded applications.
>>> import sched, time >>> s = sched.scheduler(time.time, time.sleep) >>> def print_time(): print "From print_time", time.time() ... >>> def print_some_times(): ... print time.time() ... s.enter(5, 1, print_time, ()) ... s.enter(10, 1, print_time, ()) ... s.run() ... print time.time() ... >>> print_some_times() 930343690.257 From print_time 930343695.274 From print_time 930343700.273 930343700.276
In multi-threaded environments, the
scheduler class has limitations
with respect to thread-safety, inability to insert a new task before
the one currently pending in a running scheduler, and holding up the main
thread until the event queue is empty. Instead, the preferred approach
is to use the
threading.Timer class instead.
>>> import time >>> from threading import Timer >>> def print_time(): ... print "From print_time", time.time() ... >>> def print_some_times(): ... print time.time() ... Timer(5, print_time, ()).start() ... Timer(10, print_time, ()).start() ... time.sleep(11) # sleep while time-delay events execute ... print time.time() ... >>> print_some_times() 930343690.257 From print_time 930343695.274 From print_time 930343700.273 930343701.301
8.8.1. Scheduler Objects¶
scheduler instances have the following methods and attributes:
enterabs(time, priority, action, argument)¶
Schedule a new event. The time argument should be a numeric type compatible with the return value of the timefunc function passed to the constructor. Events scheduled for the same time will be executed in the order of their priority.
Executing the event means executing
action(*argument). argument must be a sequence holding the parameters for action.
Return value is an event which may be used for later cancellation of the event (see
enter(delay, priority, action, argument)¶
Schedule an event for delay more time units. Other than the relative time, the other arguments, the effect and the return value are the same as those for
Remove the event from the queue. If event is not an event currently in the queue, this method will raise a
Return true if the event queue is empty.
Run all scheduled events. This function will wait (using the
delayfunc()function passed to the constructor) for the next event, then execute it and so on until there are no more scheduled events.
Either action or delayfunc can raise an exception. In either case, the scheduler will maintain a consistent state and propagate the exception. If an exception is raised by action, the event will not be attempted in future calls to
If a sequence of events takes longer to run than the time available before the next event, the scheduler will simply fall behind. No events will be dropped; the calling code is responsible for canceling events which are no longer pertinent.