python計算貸款購房月供、利息

def monthlyPayment(principal, year_rate, year_duration):
    monthly_rate = year_rate / (12 * 100)   # convert 4.9 to 0.049 and  monthly interest rate
    month_amounts =  year_duration * 12

    # 每月月供
    monthly_payment = (principal * monthly_rate * (1 + monthly_rate) ** month_amounts) / (
    (1 + monthly_rate) ** month_amounts - 1)
    #總利息
    total_interest_payable = monthly_payment * month_amounts - principal
    print('-----------------------------------')
    print ('Total interest payable is %.2f ' % total_interest_payable)

    for i in range (1, month_amounts + 1):
        #每月應還利息
        monthly_interest_payable = principal * monthly_rate * ((1 + monthly_rate) ** month_amounts - (1 + monthly_rate) ** (i - 1 ))/ ((1 + monthly_rate) ** month_amounts -1)
        #每月應還本金
        monthly_principal_payable = principal * monthly_rate * (1 + monthly_rate) ** (i - 1)/ ((1 + monthly_rate) ** month_amounts -1)
        #每月利息佔比
        monthly_interest_percentage = monthly_interest_payable * 100 / monthly_payment

        print('-----------------------------------')
        print ('%dth monthly payment is : %.2f (Interest: %.2f and Principal: %.2f)' % (i, monthly_payment,monthly_interest_payable,monthly_principal_payable))
        print('%dth month interest percentage is %.2f %%' % (i,monthly_interest_percentage))

    return


if __name__ == '__main__':
    principal = int(input('Please input your loan amounts:'))
    year_rate = float(input('Please input Year Debt Interest Rate:(such as 4.9,it means 4.9%)'))
    year_duration = int(input('Please input Debt Year Duration:'))
    monthlyPayment(principal, year_rate, year_duration)