def __index_query(query, key: str) -> float:
    """ Returns a property of the query class, keyed by a string.
        The key must be one of:
            ['Memory', 'Duration', 'Bytes Processed', 'Bytes Billed']

        Args:
            query (BigQueryResult): A BigQuery result class
            key (string): A key of the BigQueryResult object

        Returns:
            (float): The value in `query` corresponding to the key.
    """
    ResultDict = {
        "Memory": query.memory_usage(),
        "Duration": query.duration,
        "Bytes Processed": query.bytes_processed,
        "Bytes Billed": query.bytes_billed,
    }
    return ResultDict[key]