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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_class(schema_name):
 """ 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. """

    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