code: def __assert_field_mapping(self, mapping):
          
          passed_keys = set(mapping.keys())
          class_fields = set(self.FIELDS)
  
          if passed_keys != class_fields:
              raise ValueError('\n'.join([
                  "{0} got different fields from expected".format(
                      self.__class__),
                  "  got     : {0}".format(list(sorted(passed_keys))),
                  "  expected: {0}".format(list(sorted(class_fields)))]))
docs: Assert that mapping.keys() == FIELDS.
  
          The programmer is not supposed to pass extra/less number of fields