invest.py

MONTHLY_INVESTMENT = 188.0
MONTHS_TO_INVEST = 120

YEARLY_INTEREST = 0.04
MONTHLY_INTEREST = (1 + YEARLY_INTEREST)**(1.0/12) - 1


def main():
    balance = 0
    for month in xrange(MONTHS_TO_INVEST):
        balance *= 1 + MONTHLY_INTEREST
        balance += MONTHLY_INVESTMENT

    print balance        

    principal = MONTHLY_INVESTMENT * MONTHS_TO_INVEST
    interest = balance - principal
    print principal, interest


if __name__ == "__main__":
    main()