"""Return a datetime that is N units before/after a base datetime.
e.g. 3 Wednesdays from base datetime, 2 weeks from base date, 10
years before base datetime, 13 minutes after base datetime, etc...
"""Return a datetime that is N units before/after a base datetime.
e.g. 3 Wednesdays from base datetime, 2 weeks from base date, 10
years before base datetime, 13 minutes after base datetime, etc...