Generate a list of datetimes between an interval

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 

Answer 2

Try this:

from datetime import datetime from dateutil.relativedelta import relativedelta  def date_range(start_date, end_date, increment, period):     result = []     nxt = start_date     delta = relativedelta(**{period:increment})     while nxt <= end_date:         result.append(nxt)         nxt += delta     return result 

The example in the question, "every 8 hours between now and tomorrow 19:00" would be written like this:

start_date = datetime.now() end_date = start_date + relativedelta(days=1) end_date = end_date.replace(hour=19, minute=0, second=0, microsecond=0) date_range(start_date, end_date, 8, 'hours')     

Notice that the valid values for period are those defined for the relativedelta relative information, namely: 'years', 'months', 'weeks', 'days', 'hours', 'minutes', 'seconds', 'microseconds'.

My solution returns a list, as required in the question. If you don't need all the elements at once you can use generators, as in @MartijnPieters answer.