How to round a datetime up to a specific time?

Question

Given a datetime object, how do I round it up to the next occurrence of 8AM PST?

Make a new datetime, use input from the current datetime year, month, day and set hours, mins, seconds as 8, 0, 0 respectively — Ian, Feb 24 '16 at 18:16
@Ian: This would always be today's 8AM. To always round up, you need to add another day on top unless it is before 8AM. — jsfan, Feb 24 '16 at 18:19
related: [Rounding up to nearest 30 minutes in python](http://stackoverflow.com/q/32723150/4279) — jfs, Feb 25 '16 at 12:46

Brendan Abel · Answer 1 · 2016-02-24T18:44:30.390

3

Just test whether the time is before or after 8, then add a day if it's after and construct a new datetime.

import datetime

def round_datetime(dt):
    t = datetime.time(8)
    # If time is after 8am, add a day.
    if dt.time() > datetime.time(8):
        dt += datetime.timedelta(days=1)
    return datetime.datetime.combine(dt, t)

edited Feb 24 '16 at 18:44

answered Feb 24 '16 at 18:43

Brendan Abel

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Thanks, I didn't realize you could split up the date and time like that. – camomilk Feb 24 '16 at 19:49
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if the input is a timezone-aware datetime object then it is more complex (your code is ok if the input is a naive datetime object). – jfs Feb 25 '16 at 12:41

score 3 · Accepted Answer · edited May 23 '17 at 11:53

If the result is a timezone-aware datetime object in a timezone with a non-fixed UTC offset then you can't just call .replace() or .combine() -- it may create a datetime with a wrong UTC offset. The issue is similar to How do I get the UTC time of "midnight" for a given timezone? (00:00 is used instead of 08:00).

Assuming 8AM always exists and unambiguous in PST:

from datetime import datetime, time as datetime_time, timedelta
import pytz # $ pip install pytz

def next_8am_in_pst(aware_dt, tz=pytz.timezone('America/Los_Angeles')):
    pst_aware_dt = tz.normalize(aware_dt.astimezone(tz)) # convert to PST
    naive_dt = round_up_to_8am(pst_aware_dt.replace(tzinfo=None))
    return tz.localize(naive_dt, is_dst=None)

def round_up_to_8am(dt):
    rounded = datetime.combine(dt, datetime_time(8))
    return rounded + timedelta(rounded < dt)

Example:

>>> str(next_8am_in_pst(datetime.now(pytz.utc))) 
'2016-02-25 08:00:00-08:00'

Thanks, this works across daylight saving boundaries. – camomilk Mar 10 '16 at 20:28 — camomilk, Mar 10 '16 at 20:28

score 0 · Answer 3 · answered Feb 24 '16 at 18:42

0

I made an answer based on some ideas from the comments:

def nextDay(d):
    pstTime = d.astimezone(pytz.timezone('US/Pacific'))
    pstTime = pstTime.replace(hour=8, minute=0, second=0, microsecond=0)

    if pstTime < d:
        pstTime += datetime.timedelta(days=1)

    return pstTime

answered Feb 24 '16 at 18:42

camomilk

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it may fail around dates with a DST transition – jfs Feb 25 '16 at 12:42

How to round a datetime up to a specific time?

3 Answers3