python - 用 Python 比较贷款

Question

我正在为我的 Python 类(class)做作业。我几乎弄明白了，但我的输出与原始问题中显示的略有不同。当利率为 5.125% 时，我的月供为 189.29，但问题的输出为 188.28。没有格式的原始数字是189.286。我想也许在金融系统中，他们只是简单地削减小数而不是使用“舍入”。我不确定在 Python 中是否有任何方法可以做到这一点。问题就在这里。

编写一个程序，让用户输入贷款金额和贷款年限，并显示每个利率从 5% 到 8% 的每月还款额和总还款额，增量为 1/8。

输入:

Loan Amount: 10000
Number of Years: 5

输出:

Interest Rate   Monthly Payment Total Payment
5.000%          188.71          11322.74
5.125%          189.29          11357.13
...    
7.875%          202.17          12129.97
8.000%          202.76          12165.84

代码:

LoanAmount = float(input("Loan Amount:"))
NumOfYears = float(input("Number of Years:"))
AnnualRate = float(5.0)
print("\nInterest Rate\t" + "Monthly Payment\t" + "Total Payment")
while (AnnualRate <= 8.0):
    MonthlyRate = float(AnnualRate/1200)
    MonthlyPayment = float(LoanAmount * MonthlyRate / (1- 1/ pow(1+MonthlyRate, NumOfYears *12)))
    TotalPayment = format(MonthlyPayment * NumOfYears * 12, ".2f")
    print (format(AnnualRate, ".3f"), end = "%\t\t")
    print (format(MonthlyPayment, ".2f"), end = "\t\t")
    print(TotalPayment, end = "\n")
    AnnualRate += 1.0/8

Answer 1

当您处理金钱时，请使用 decimal模块。这允许许多不同的 rounding modes .例如，向下舍入:

import decimal

payment = decimal.Decimal('189.286')
with decimal.localcontext() as ctx:
    ctx.rounding = decimal.ROUND_DOWN
    print(round(payment, 2))

打印:

189.28

Bankers' rounding会是:

decimal.ROUND_HALF_EVEN

Round to nearest with ties going to nearest even integer.

with decimal.localcontext() as ctx:
    ctx.rounding = decimal.ROUND_HALF_EVEN
    print(round(payment, 2))