In Python, how can I put a thread to sleep until a specific time?

Question

I know that I can cause a thread to sleep for a specific amount of time with:

time.sleep(NUM)

How can I make a thread sleep until 2AM? Do I have to do math to determine the number of seconds until 2AM? Or is there some library function?

( Yes, I know about cron and equivalent systems in Windows, but I want to sleep my thread in python proper and not rely on external stimulus or process signals.)

Answer 1

Here's a half-ass solution that doesn't account for clock jitter or adjustment of the clock. See comments for ways to get rid of that.

import time
import datetime

# if for some reason this script is still running
# after a year, we'll stop after 365 days
for i in xrange(0,365):
    # sleep until 2AM
    t = datetime.datetime.today()
    future = datetime.datetime(t.year,t.month,t.day+(t.hour >= 2 ),2,0)
    time.sleep((future-t).seconds)

    # do 2AM stuff

Answer 2

One possible approach is to sleep for an hour. Every hour, check if the time is in the middle of the night. If so, proceed with your operation. If not, sleep for another hour and continue.

If the user were to change their clock in the middle of the day, this approach would reflect that change. While it requires slightly more resources, it should be negligible.