def LOG(number, base):
    """
    Calculates the log of a number in the specified base and returns the result as a double.
    See https://docs.mongodb.com/manual/reference/operator/aggregation/log/
    for more details
    :param number: The number or field of number
    :param base: The base of log operation
    :return: Aggregation operator
    """
    return {'$log': [number, base]}