code: def datetime_round(dt, period, start=None):
  	
  	result = datetime_mod(dt, period, start)
  	if abs(dt - result) >= period // 2:
  		result += period
  	return result
docs: Find the nearest even period for the specified date/time.
  
  	>>> datetime_round(datetime.datetime(2004, 11, 13, 8, 11, 13),
  	...     datetime.timedelta(hours = 1))
  	datetime.datetime(2004, 11, 13, 8, 0)
  	>>> datetime_round(datetime.datetime(2004, 11, 13, 8, 31, 13),
  	...     datetime.timedelta(hours = 1))
  	datetime.datetime(2004, 11, 13, 9, 0)
  	>>> datetime_round(datetime.datetime(2004, 11, 13, 8, 30),
  	...     datetime.timedelta(hours = 1))
  	datetime.datetime(2004, 11, 13, 9, 0)