code: def _ValidateTimeRange(timerange):
    
    if len(timerange) != 2:
      raise ValueError("Timerange should be a sequence with 2 items.")
  
    (start, end) = timerange
    precondition.AssertOptionalType(start, rdfvalue.RDFDatetime)
    precondition.AssertOptionalType(end, rdfvalue.RDFDatetime)
docs: Parses a timerange argument and always returns non-None timerange.