Just a simple, fail-safe in­ter­pre­ta­ti­on of time deltas using crontab-like syntax using python’s horrible regular expression syntax.

import re
from datetime import timedelta

def tdelta(input):

    keys = ["weeks", "days", "hours", "minutes"]
    regex = "".join(["((?P<%s>\d+)%s ?)?" % (k, k[0]) for k in keys])
    kwargs = {}
    for k,v in re.match(regex, input).groupdict(default="0").items():
        kwargs[k] = int(v)
    return timedelta(**kwargs)

>>> print tdelta("3w")
21 days, 0:00:00
>>> print tdelta("3w 12h 57m")
21 days, 12:57:00

walk-through

datetime‘s timedelta object provides a fairly simple interface to add, substract and compare datetime-objects in python. In my example, I am using only, weeks, days, hours and minutes, but timedelta can also handle seconds and/or mil­li­se­conds. Add them to keys, when you need them. I was too lazy to write down the whole regex. Building the regex dynamic has also the advantage to extend or limit the keywords. Actually, you simply search the input in the order of keys and match the value in front of the short character. Calling the groupdict-function with default=”0” is required, to have proper handling of missing arguments. Finally, passing kwargs as known-arguments dictionary (via **) to timedelta.