def lift_calc(PPV, PRE):
    """
    Calculate lift score.

    :param PPV:  precision or positive predictive value
    :type PPV : float
    :param PRE: Prevalence
    :type PRE : float
    :return: lift score as float
    """
    try:
        return PPV / PRE
    except (ZeroDivisionError, TypeError):
        return 'None'
