round a datetime to minutes

round_to_minutes.py

import datetime


def floor_to_minute(time, minutes):
    time = time - datetime.timedelta(
        minutes=time.minute % minutes,
        seconds=time.second,
        microseconds=time.microsecond)

    return time


def ceil_to_minute(time, minutes):
    time += datetime.timedelta(minutes=minutes)
    time = floor_to_minute(time, minutes)

    return time


def minute_interval(starttime, endtime, step_width, include_start=False):
    time = starttime

    rounding_func = floor_to_minute if include_start else ceil_to_minute
    time = rounding_func(time, step_width)

    steps = [time]

    while True:
        time += datetime.timedelta(minutes=step_width)
        if time > endtime:
            return steps
        steps.append(time)

if __name__ == '__main__':
    from pprint import pprint

    starttime = datetime.datetime(2014, 9, 18, 8, 5, 0)
    endtime = starttime + datetime.timedelta(hours=3.5)

    print(starttime, floor_to_minute(starttime, 15))
    print(starttime, ceil_to_minute(starttime, 15))

    print(starttime, endtime)
    pprint(minute_interval(starttime, endtime, 15, True))

$ python round_to_minutes.py

(datetime.datetime(2014, 9, 18, 8, 5), datetime.datetime(2014, 9, 18, 8, 0))
(datetime.datetime(2014, 9, 18, 8, 5), datetime.datetime(2014, 9, 18, 8, 15))
(datetime.datetime(2014, 9, 18, 8, 5), datetime.datetime(2014, 9, 18, 11, 35))
[datetime.datetime(2014, 9, 18, 8, 0),
 datetime.datetime(2014, 9, 18, 8, 15),
 datetime.datetime(2014, 9, 18, 8, 30),
 datetime.datetime(2014, 9, 18, 8, 45),
 datetime.datetime(2014, 9, 18, 9, 0),
 datetime.datetime(2014, 9, 18, 9, 15),
 datetime.datetime(2014, 9, 18, 9, 30),
 datetime.datetime(2014, 9, 18, 9, 45),
 datetime.datetime(2014, 9, 18, 10, 0),
 datetime.datetime(2014, 9, 18, 10, 15),
 datetime.datetime(2014, 9, 18, 10, 30),
 datetime.datetime(2014, 9, 18, 10, 45),
 datetime.datetime(2014, 9, 18, 11, 0),
 datetime.datetime(2014, 9, 18, 11, 15),
 datetime.datetime(2014, 9, 18, 11, 30)]