Calculate conditional entropy.

    :param classes: confusion matrix classes
    :type classes : list
    :param table: confusion matrix table
    :type table : dict
    :param P: condition positive
    :type P : dict
    :param POP: population
    :type POP : dict
    :return: conditional entropy as float

def conditional_entropy_calc(classes, table, P, POP):
    """
    Calculate conditional entropy.

    :param classes: confusion matrix classes
    :type classes : list
    :param table: confusion matrix table
    :type table : dict
    :param P: condition positive
    :type P : dict
    :param POP: population
    :type POP : dict
    :return: conditional entropy as float
    """
    try:
        result = 0
        for i in classes:
            temp = 0
            for index, j in enumerate(classes):
                p_prime = 0
                if P[i] != 0:
                    p_prime = table[i][j] / P[i]
                if p_prime != 0:
                    temp += p_prime * math.log(p_prime, 2)
            result += temp * (P[i] / POP[i])
        return -result
    except Exception:
        return "None"