multithreading - Sleeping a Thread until certain time in Python -

i've written script creates threads sleep until time of day before sending email. run @ 4pm on day script run, others run @ 7am next morning.

my problem threads supposed run @ 4pm won't run until 5pm or 6pm, whereas ones @ 7am run right on time. script typically started between 10am-1pm. i'm using python 2.6.6

the code, in nutshell, follows:

from datetime import datetime, timedelta import threading  def main():   today = datetime.now()   today_at_4pm = today.replace(hour=16, minute=0, second=0)    tomorrow = today + timedelta(days=1)   tomorrow_at_7am = tomorrow.replace(hour=7, minute=0, second=0)    message = "some message"   threading.thread(target=dispatchemail, args=(message, today_at_4pm)).start()   threading.thread(target=dispatchemail, args=(message, tomorrow_at_7am)).start()   def dispatchemail(message, time_to_send):   = datetime.now()    if < time_to_send:     time_diff = time_to_send -     diff_in_seconds = (time_diff.days * 86400) + time_diff.seconds     sleep(diff_in_seconds)    sendemail(message)  def sendemail(message):   print message  if __name__ == '__main__': main() 

i can't pin down problem because it's inconsistent when sends , don't have problem running on short time periods. diff_in_seconds calculation appears accurate.

i think error lies in sleep part or in misunderstanding of how threads work. appreciated.

for think should seperate scripts , use crontasks -- i'd prefer not because of how actual contents of message being read/tracked files.

update

i found threading.timer method via python sched docs. allows me run function after period of time. moved sleep time calculation out of dispatchemail allowed me rid of it:

def timedifference(now, time_to_send):   if < time_to_send:     time_difference = time_to_send -     return (time_difference.days * 86400) + time_difference.seconds   else:     return 0  time_until_4pm = timedifference(datetime.now(), today_at_4pm) time_until_7am = timedifference(datetime.now(), tomorrow_at_7am)  threading.timer(time_until_4pm, sendemail, (message)) threading.timer(time_until_7am, sendemail, (message)) 

are there nuances need aware about?

don't use thread sleeping. absolutely wrong approach problem. if don't want use crons (i assume mean literal linux cron jobs), use https://docs.python.org/2/library/sched.html