Python Basics Exercises: Functions and Loops (Summary)

import sys

#--------------------------- functions ----------------------------------------
def compound_interest_core(principal_amount, rate_per_period, period):
    return principal_amount * (1 + rate_per_period) ** period


def annual_interest(amount, rate, periods):
    for year in range(1, periods+1):
        year_amount = compound_interest_core(amount, rate, year)
        print(f'Year {year}: ${year_amount:,.2f}')

    # output interest earned
    print((f'Total interest earned after {periods} years with annual compounding: '
           f'${year_amount - amount:,.2f}'))


def monthly_interest(amount, rate, periods):
    principal_amount = amount
    months = periods * 12
    monthly_rate = rate / 12

    for month in range(1, months+1):
        amount = compound_interest_core(amount, monthly_rate, 1)
        if month % 12 == 0:
            year = month // 12
            print(f'End of Year {year}: ${amount:,.2f}')

    # Output interest earned
    print((f'Total interest earned after {periods} years with monthly compounding: '
           f'${amount - principal_amount:,.2f}'))
#------------------------- end of functions -----------------------------------

while True:
    compounds = ('monthly', 'annually')

    compound_period = input('Enter the compound period? monthly or annually: ').lower()
    if not compound_period in compounds:
        print('Aceptable inputs: monthly or annually. try again!\n')
        continue

    principal_amount = float(input('Principal Amount: '))
    interest_rate = float(input('Interest Rate: '))
    periods = int(input('Time: '))

    if compound_period == 'monthly':
        monthly_interest(principal_amount, interest_rate, periods)
    elif compound_period == 'annually':
        annual_interest(principal_amount, interest_rate, periods)

    print()

    while True:
        choices_for_exit_prompt = ('y', 'n')
        restart_calc = input('Restart? y/n: ')
        if not restart_calc in choices_for_exit_prompt:
            print('Acceptable input: y/n. try again!\n')
            continue

        if restart_calc == 'n': sys.exit('Exiting...')

        print('Restarting...\n')
        break