def TTPN_calc(item1, item2):
    """
    Calculate TPR,TNR,PPV,NPV.

    :param item1: item1 in fractional expression
    :type item1 : int
    :param item2: item2 in fractional expression
    :type item2: int
    :return: result as float
    """
    try:
        result = item1 / (item1 + item2)
        return result
    except ZeroDivisionError:
        return "None"