code: def rationalize_until(until=None):
      
      if until is None:
          until = "+inf"
      elif isinstance(until, datetime):
          until = to_unix(until)
      elif isinstance(until, timedelta):
          until = to_unix((datetime.utcnow() + until))
      return until
docs: Rationalizes the `until` argument used by other functions. This function
      accepts datetime and timedelta instances as well as integers representing
      epoch values.