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I cannot seem to find a simple example of how to schedule an event in Python.

I want to be able to pass a date and time string as an argument into a function.

For example:

String: "m/d/Y HH:MM" would set the time for a future function to run, after the code has been executed. So, like a function that is waiting to go off after I run it.

It seems like the main problem is formatting the string correctly, but a simple example would really help to see how to 'schedule' a function to run.

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You don give enough context to understand what are you trying to do in a larger frame - but, generally speaking - "this is not how it works" in Python.

An "ordinary" Python program is a single-threaded, synchronous program - it will run one task, after another, after another, when everything is done, the program exits, and the interpreter exits along with it.

so, something along (with a fictitious "schedule" function):

def main():
    print("Hello World")
    schedule(60, main)

main()

would not work in Python, if the call to schedule would return immediately - the main function would exit, and the program would try to resume after the main() call, and terminate. There needs to be a piece of code left running, which can count time, and delays, maybe receive network or user generated events, and dispatch them to previously arranged callback functions in order for a program to keep running.

Such a piece of code, which can account for time and dispatch calls, is usually called a "reactor" - and there is none running in a plain Python program. Unlike, say, in a JavaScript program, where the browser, or other JavaScript environment provides such hosting by default.

That is why most Python web or network frameworks, all GUI toolkits, provide such a core - it is usually called at the end of the one main's script and is a method or function named mainloop or serve_forever, start and so on. From that point on, your main script, which had set the appropriate callbacks, scheduled things and so on, stops - the reactor will be the piece of code calling things.

That is where I say your question misses the context of what you want to do: at first you just want to test some scheduling - but afterwards you will want that inside a larger system - that system should be built using an appropriated framework for your "real task" at hand, for example Django, tornado, pyramid, if it is a web-server system, gtk, Qt, Tk if it is a GUI program, PyOgre, kivy, pyglet if it is a multimedia program, twisted for a generic network server of another protocol, or some other thing, like celery or camaelia - these are only general examples.

That said, Python's standard library does offer a "generic" scheduler function - it does implement such a loop, with the bare core of functionality. If you are doing nothing else, and nothing fancy, it will block there until it reaches the time to call your scheduled function, at which point it will exit, and resume the control to your main program. If your called function schedule other things, it will continue running, and so on.

See the documentation and example at: http://docs.python.org/2/library/sched.html

You can use functions from the datetime module instead of time.time to set r absolute timings as you asking for. Also check the documentation there to threading.Timer - which in a naively way can do more or less what you have in mind, if you want to run a simple function after a given delay, in parallel to whatever other code is running and don't want to rewrite your application to be event based - but simpler as it may seen, it will have many drawbacks in a larger system - you should pick one of the frameworks listed.

于 2013-03-24T11:13:04.667 回答