code: def normalize(input, case_mapping=protocol.DEFAULT_CASE_MAPPING):
      
      if case_mapping not in protocol.CASE_MAPPINGS:
          raise pydle.protocol.ProtocolViolation('Unknown case mapping ({})'.format(case_mapping))
  
      input = input.lower()
  
      if case_mapping in ('rfc1459', 'rfc1459-strict'):
          input = input.replace('{', '[').replace('}', ']').replace('|', '\\')
      if case_mapping == 'rfc1459':
          input = input.replace('~', '^')
  
      return input
docs: Normalize input according to case mapping.