Return a datetime set to be the nth interation of some unit of time given by unit. Acceptable values for unit are "month", "quarter", and "year".

Week days must be passed to this function. Setting the unit to 'month', the week day to 'monday', and nth to 3 will return the 3rd Monday of the month, for example.

Times are stripped from the input datetime.

Arguments:

def datetime.nth_of(
  dt: <datetime> = None,
  unit: <str> = None, # 'hour', 'day', 'week', 'month', or 'year'
  day_of_week: <str> = None, # 'monday', 'tuesday', ...
  nth: <dec> = None,
):

Returns <datetime>.

Example:

long_long_ago = datetime.from_date_and_time(
  year=1995,
  month=1,
  day=15,
  hour=0,
  minute=0,
  second=0)

# third_monday_1995 == Monday January 16 1995 00:00:00
third_monday_1995 = datetime.nth_of(dt=long_long_ago, unit='year',
  day_of_week='monday', nth=3)