Python 3.5 - 每年贷款余额

Question

我是Python的新手，正在尝试计算并输出基于4.5％年利率的贷款年度余额。病程5年和原则= 1000，但我只能做到每年支付的金额，但资产负债不匹配这应该是要求：

 balance total payment 
year 1 817  223 
year 2 626  447 
year 3 427  671 
year 4 218  894 
year 5 0  1118 

我的计划是：

def monthlyPayments(principle,annual_interest_rate,duration): 
    global r, n 

    r=(annual_interest_rate/100)/12 #monthly interest rate 
    n=duration*pm#Total number of monthly payments for duration of loan 
    f1=pow(1+r,n) 
    f2=r*f1 
    f3=pow(1+r,n) 
    f4=f3-1 
    f5=f2/f4 
    monthlyPayment=principle*f5 

    return monthlyPayment 

def balance(principle,annual_interest_rate,duration,pm): 
    f1=pow(1+r,n) 
    f2=pow(1+r,pm) 
    f3=f1-1 
    f4=f1-f2 
    f5=f4/f3 
    remainingLoanBalance=principle*f5 

    return remainingLoanBalance 

principle=1000.0 
annual_interest_rate=4.5 
duration=5 
pm=12#payments made 
monthlyPayments=monthlyPayments(principle,annual_interest_rate,duration) 
totalPayment=monthlyPayments*pm 
balance =balance(principle,annual_interest_rate,duration,pm) 
print("LOAN AMOUNT:",principle,"INTEREST RATE (PERCENT):",annual_interest_rate, "\nDURATION (YEARS):", duration, "MONTHLY PAYMENT:", int(monthlyPayments)) 

for i in range(1,duration+1): 
    print("YEAR:" ,i, "BALANCE:", int(balance), "TOTAL PAYMENT", int(totalPayment)) 

    totalPayment=totalPayment+monthlyPayments*pm 
    balance=balance-monthlyPayments*pm 

Answer 1

尝试numpy，你会爱上它的。 ;）

np.pmt（） - 计算每月还款

np.fv（） - 计算使用numpy的）未来价值

码（：

from __future__ import print_function 
import numpy as np 

amount = 1000 
int_rate = 4.5/100 
term = 5 
nper = 12 
mtly_pmt = -np.pmt(int_rate/nper, term*nper, amount) 

fmt = 'year {0:2d} {1:8.2f} {2:8.2f}' 

for y in range(1, term + 1): 
    print(fmt.format(
      y, 
      np.fv(int_rate/nper, y*nper, mtly_pmt, -amount), 
      mtly_pmt * y * nper 
     ) 
    ) 

输出：

year 1 817.55 223.72 
year 2 626.72 447.43 
year 3 427.12 671.15 
year 4 218.36 894.86 
year 5 -0.00 1118.58 

代码（不numpy的）：

from __future__ import print_function 

# compute monthly payment 
def pmt(rate, nper, pv): 
    """ 
    rate - annual interest rate 
    nper - # of periodic payments 
    pv  - present value (principal loan amount) 
    """ 
    return (rate * pv)/(1 - (1 + rate)**(-nper)) 

# compute future value (remaining balance) 
def fv(rate, nper, pmt, pv): 
    """ 
    rate - annual interest rate 
    nper - # of periodic payments 
    pmt  - monthly payment 
    pv  - present value (principal loan amount) 

    r1 = (1 + interest_rate) - will be used a few times below 
    """ 
    r1 = 1 + rate 
    return pv * r1**nper - pmt * (r1**nper -1)/rate 


amount = 1000 
int_rate = 4.5/100 
term = 5 
nper = 12 
mtly_pmt = round(pmt(int_rate/nper, term*nper, amount), 2) 

fmt = 'year {0:2d} {1:8.2f} {2:8.2f}' 

for y in range(1, term + 1): 
    print(fmt.format(
      y, 
      fv(int_rate/nper, y*nper, mtly_pmt, amount), 
      mtly_pmt * y * nper, 
     ) 
    ) 

输出：

year 1 817.59 223.68 
year 2 626.80 447.36 
year 3 427.24 671.04 
year 4 218.52 894.72 
year 5  0.20 1118.40