Question

I want to have a loop be executed once every minute when datetime.utcnow().second is zero.
So far I have this

while True:
    while datetime.utcnow().second != 0: pass
    do_something()

But the problem with this is that I am wasting cpu processes. I would use time.sleep(60), but I don’t know how it would sync with the UTC clock, because time.sleep(60) could stray from the official UTC time as time passes.

Answer 1

Best way I can think of would be to sleep until the next minute:

while True:
    sleeptime = 60 - datetime.utcnow().second
    time.sleep(sleeptime)
    ...

If you want to be really precise:

while True:
    t = datetime.utcnow()
    sleeptime = 60 - (t.second + t.microsecond/1000000.0)
    time.sleep(sleeptime)
    ...

This sleeps for exactly the amount of time necessary to reach the next minute, with subsecond precision.

EDITED to fix minute rollover bug.