Question

Given two datetimes (start_date and end_date), I’d like to generate a list of other datetimes between these two dates, the new datetimes being separated by a variable interval. e.g. every 4 days between 2011-10-10 and 2011-12-12 or every 8 hours between now and tomorrow 19p.m.

Maybe something roughly equivalent to the Dateperiod PHP class.

What would be the most efficient way to accomplish this in Python?

Answer 1

Use datetime.timedelta:

from datetime import date, datetime, timedelta

def perdelta(start, end, delta):
    curr = start
    while curr < end:
        yield curr
        curr += delta

>>> for result in perdelta(date(2011, 10, 10), date(2011, 12, 12), timedelta(days=4)):
...     print result
...
2011-10-10
2011-10-14
2011-10-18
2011-10-22
2011-10-26
2011-10-30
2011-11-03
2011-11-07
2011-11-11
2011-11-15
2011-11-19
2011-11-23
2011-11-27
2011-12-01
2011-12-05
2011-12-09

Works for both dates and datetime objects. Your second example:

>>> for result in perdelta(datetime.now(),
...         datetime.now().replace(hour=19) + timedelta(days=1),
...         timedelta(hours=8)):
...     print result
... 
2012-05-21 17:25:47.668022
2012-05-22 01:25:47.668022
2012-05-22 09:25:47.668022
2012-05-22 17:25:47.668022