def STD_DEV_SAMP(*expression):
    """
    Calculates the sample standard deviation of the input values.
    Use if the values encompass a sample of a population of data from which to generalize about the population.
    See https://docs.mongodb.com/manual/reference/operator/aggregation/stdDevSamp/
    for more details
    :param expression: expression/expressions
    :return: Aggregation operator
    """
    return {'$stdDevSamp': list(expression)} if len(expression) > 1 else {'$stdDevSamp': expression[0]} if expression else {}