原文链接：https://blog.csdn.net/sinat_37967865/article/details/94744873

from decimal import Decimal

from prettytable import PrettyTable
import copy
from dealFloat import float_deal # Decimal格式


principal = Decimal('1000.00') # 本金
annual_rate = Decimal('0.115') # 年化利率
term_rate = annual_rate / Decimal('12') # 月利率
day_rate = annual_rate / Decimal('12') /Decimal('30') # 日利率


repayPattern = {
"MCAT": "随借随还,按日计息",
"BFTO": "利随本清,按日计息",
"MIRD": "按月付息到期还本",
"EPEI": "等本等息,按月付息", # 对借款人最不利
"MCEP": "等额本金,按月付息", # 借款总利息最低
"MCEI": "等额等息,按月付息"
}

line = PrettyTable(["期数", "还款本息", "当期本金", "当期利息","剩余本金","还款方式"])

#line.align["期数"] = "1" # 以期数字段左对齐
#line.padding_width = 2 # 填充宽度(字段间隔)


# "EPEI": "等本等息,按月付息" 每期利息和本金一样,最后一期本金为上一期的剩余本金，最后一期利息为总利息-已还利息
def get_EPEI(num):
show = copy.deepcopy(line)
term_int = float_deal(principal * term_rate) # 每期还利息（2位小数）
total_int = float_deal(principal*term_rate*num) # 总利息（2位小数）
term_prin = float_deal(principal / num) # 每期还本金（2位小数）
prin = principal # 初始化剩余本金为借款本金
for i in range(1,num+1):
# 如果是最后一期，还款本金为上一期的剩余本金; 利息为总利息-已还利息
if i == num:
term_prin = prin
term_int = total_int - (term_int*(num-1))
term_amt = term_prin + term_int
prin = prin - term_prin # 剩余本金=上期剩余本金-当期还本金
show.add_row([i, term_amt, term_prin, term_int, prin,'EPEI'])
print('等本等息总利息为：',total_int)
print(show)


# "MIRD": "按月付息到期还本" 最后一期还本金，每期利息固定
def get_MIRD(num):
show = copy.deepcopy(line)
term_int = float_deal(principal*term_rate)
term_prin = float_deal(0.0)
total_int = float_deal(principal * term_rate * num) # 总利息（2位小数）
prin = principal
for i in range(1,num+1):
# 如果是最后一期，还款本金为上一期的剩余本金; 利息为总利息-已还利息
if i == num:
term_prin = prin
term_int = total_int - (term_int*(num-1))
term_amt = term_prin + term_int
prin = prin - term_prin # 剩余本金=上期剩余本金-当期还本金
show.add_row([i, term_amt, term_prin, term_int, prin, 'MIRD'])
print('按月付息到期还本总利息为：', total_int)
print(show)


# "等额本金,按月付息"
def get_MCEP(num):
## 每月本金相同，利息递减，相当于剩余本金的利息,每期利息固定：上一期本金*利率
show = copy.deepcopy(line)
term_prin = float_deal(principal / num) # 每期还本金（2位小数）
prin = principal
total_int = float_deal(0.0)
for i in range(1, num + 1):
term_int = float_deal(prin * term_rate) # 每期利息固定：上一期本金*利率
# 如果是最后一期，还款本金为上一期的剩余本金;
if i == num:
term_prin = prin
term_amt = term_prin + term_int
prin = prin - term_prin # 剩余本金=上期剩余本金-当期还本金
show.add_row([i, term_amt, term_prin, term_int, prin,'MCEP'])
total_int = float_deal(total_int + term_int)
print('等额本金总利息为：', total_int)
print(show)


# "MCEI": "等额本息,按月付息"
def get_MCEI(num):
# 本金+利息保持相同，本金逐月递增，利息逐月递减，月还款数不变。
show = copy.deepcopy(line)
term_amt = float_deal((principal*term_rate*(1+term_rate)**num)/((1+term_rate)**num-1)) # 每期还款总额 **是幂运算
prin = principal
total_int = float_deal(0.0)
for i in range(1, num + 1):
term_int = float_deal(prin * term_rate) # 每期利息计算固定：上一期本金*利率
term_prin = term_amt - term_int
# 如果是最后一期，还款本金为上一期的剩余本金;
if i == num:
term_prin = prin
term_amt = term_prin + term_int
prin = prin - term_prin # 剩余本金=上期剩余本金-当期还本金
show.add_row([i, term_amt, term_prin, term_int,prin,'MCEI'])
total_int = total_int + term_int
print('等额本息总利息为：', total_int)
print(show)


# "MCAT": "随借随还,按日计息"
def get_MCAT(num,pay):
show = copy.deepcopy(line)
day_int = float_deal(pay*day_rate*num)
repay_amt = day_int + pay
re_prin = principal-pay
if pay>principal:
print("还款金额:",pay,"不能大于本金:",principal)
else:
show.add_row([1, repay_amt, pay, day_int, re_prin, 'MCAT'])
print('随借随还总利息为：', day_int)
print(show)


# "BFTO": "利随本清,按日计息"
def get_BFTO(num):
show = copy.deepcopy(line)
day_int = float_deal(principal*day_rate*num)
repay_amt = day_int + principal
show.add_row([1, repay_amt, principal, day_int, 0.0, 'BFTO'])
print('利随本清总利息为：', day_int)
print(show)


if __name__ == '__main__':
get_EPEI(24) # 等本等息,按月付息
get_MIRD(24) # 到期还本,按月付息
get_MCEP(24) # 等额本金,按月付息
get_MCEI(24) # 等额本息,按月付息
get_MCAT(720,195) # 随借随还,按日计息
get_BFTO(720) # 利随本清,按日计息