3.8.1 逾期计算
根据rank值和资产等级level计算
   if level == 10:
        if 15 < rank <= 20:
            days = 1
        elif 10 < rank <= 15:
            days = 1
        elif 5 < rank <= 10:
            days = 7
        elif 0 < rank <= 5:
            days = 60
        else:
            days = 0
    elif level == 20:
        if 15 < rank <= 20:
            days = 1
        elif 10 < rank <= 15:
            days = 1
        elif 5 < rank <= 10:
            days = 7
        elif 0 < rank <= 5:
            days = 60
        else:
            days = 0
    elif level == 30:
        if 15 < rank <= 20:
            days = 7
        elif 10 < rank <= 15:
            days = 7
        elif 5 < rank <= 10:
            days = 60
        elif 0 < rank <= 5:
            days = 60
        else:
            days = 0
    else:
        if 15 < rank <= 20:
            days = 7
        elif 10 < rank <= 15:
            days = 7
        elif 5 < rank <= 10:
            days = 60
        elif 0 < rank <= 5:
            days = 60
        else:
            days = 0