code: def periodic(seconds=0, minutes=0, hours=0, days=0, weeks=0, start_date=None,
               end_date=None):
      
      period = seconds + minutes*60 + hours*3600 + days*86400 + weeks*604800
      assert period > 0, "Must specify a positive period."
      if not start_date:
          # Saturday at midnight
          start_date = datetime.datetime(2000, 1, 1)
      return (_periodic, (period, start_date, end_date))
docs: Periodic task schedule: Use to schedule a task to run periodically,
      starting from start_date (or None to be active immediately) until end_date
      (or None to repeat forever).
  
      The period starts at the given start_date, or on Jan 1st 2000.
  
      For more details, see README.