code: def create_function_from_request_pdu(pdu):
      
      function_code = get_function_code_from_request_pdu(pdu)
      try:
          function_class = function_code_to_function_map[function_code]
      except KeyError:
          raise IllegalFunctionError(function_code)
  
      return function_class.create_from_request_pdu(pdu)
docs: Return function instance, based on request PDU.
  
      :param pdu: Array of bytes.
      :return: Instance of a function.