code: def get_class(schema_name):
      
      global _registry_loaded
      if not _registry_loaded:
          load_message_classes()
  
      try:
          return _schema_name_to_class[schema_name]
      except KeyError:
          _log.warning(
              'The schema "%s" is not in the schema registry! Either install '
              "the package with its schema definition or define a schema. "
              "Falling back to the default schema...",
              schema_name,
          )
          return Message
docs: Retrieve the message class associated with the schema name.
  
      If no match is found, the default schema is returned and a warning is logged.
  
      Args:
          schema_name (six.text_type): The name of the :class:`Message` sub-class;
              this is typically the Python path.
  
      Returns:
          Message: A sub-class of :class:`Message` to create the message from.