Simple program to calculate monthly payment and total payment

mortgage_calculator.py

import argparse

def total_payment(principal, monthly_rate, payment_months):
    return principal * (1 + monthly_rate) ** payment_months

def monthly_payment(principal, monthly_rate, payment_months):
    weighted_month = ((1 + monthly_rate) ** payment_months - 1) / monthly_rate
    return total_payment(principal, monthly_rate, payment_months) / weighted_month

print('--------------------------------------------')
print('    Mortgage monthly payment calculator')
print('--------------------------------------------')
print()

parser = argparse.ArgumentParser(
    description='Calculate the monthly payment of your mortgage')
parser.add_argument('term', metavar='n', type=int,
        help='How many years is your mortgage term')
parser.add_argument('rate', metavar='r', type=float,
        help='The yearly rate in percentage of your mortgage')
parser.add_argument('principal', metavar='P', type=float,
    help='The principal of your mortgage')

args = parser.parse_args()
monthly = monthly_payment(args.principal, args.rate / 12 / 100, args.term * 12)
total = monthly * args.term * 12

print('Term:            {}-year'.format(args.term))
print('Rate:            {}%'.format(args.rate))
print('Principal:       ${}'.format(args.principal))
print('Monthly payment: ${0:.2f}'.format( monthly))
print('Total payment:   ${0:.2f}'.format(total))