Python Simple Banking System

means = [0, 0, 0]  
loan = 0
rate = 0
pay = 0
investment = 0
annual_rate = 0


# Calculate expected return of regular investment
# The formula for calculating regular investment return is: M=a(1+x)[-1+(1+x)^n]/x;
# Where M represents the expected return, a represents the regular investment amount per period, x represents the return rate, and n represents the number of investment periods.
# Assume the user invests 300 yuan per month, which is 3600 yuan per year, with an annual return rate of 15%,
# With an investment period of 35 years, the return can be calculated as 3600(1+15%)[-1+(1+15%)^35]/15%=3648044 yuan.
def fixed_investment(inv, a_rate, y):
    global means
    inv = 12 * inv
    a_rate = a_rate / 100
    if a_rate == 0:
        expected = 0
    else:
        expected = inv * (1 + a_rate) * (pow((1 + a_rate), y) - 1) / a_rate
    print("Expected income from regular investment: %.2f" % expected)
    means[1] = expected
    return expected


def balance():
    total = 0
    for i in means:
        total += i
    print("Your total assets are: %.2f" % total)
    print("Your asset details are:\n")
    print("Deposits: %.2f" % means[0])
    print("Wealth management: %.2f" % means[1])
    print("Liabilities: %.2f" % means[2])


def saving(amount):
    global means
    if amount < 0:
        print("Deposit amount cannot be less than 0!")
    else:
        means[0] += amount
        print("Deposited: %.2f yuan" % amount)
        print("Current balance: %.2f yuan" % means[0])


def draw_money(drawing):
    global means
    if drawing < 0:
        print("Withdrawal amount cannot be less than 0!")
    elif drawing > means[0]:
        print("Withdrawal amount cannot exceed the balance!")
    else:
        means[0] -= drawing
        print("Withdrawn: %.2f yuan" % drawing)
        print("Current balance: %.2f yuan" % means[0])


def loans(loan, rate, pay, years):
    global means
    if pay < (loan - pay) * rate:
        print("You will never pay it off!!!")
    else:
        if years == 0:
            count = 0
            while loan > 0:
                loan -= pay
                loan *= (1 + rate)
                count += 1
            print("The loan will be paid off in %d years." % count)
        else:
            for _ in range(years):
                loan -= pay
                if loan == 0:
                    break
                else:
                    loan *= (1 + rate)
                    print("Your current liabilities are: %.2f" % loan)
            # means[2] = loan
            return loan


# Future financial status
def future(years):
    income = fixed_investment(investment, annual_rate, years)
    debt = loans(loan, rate, pay, years)
    captial = means[0] + income - debt
    print("Your total assets in year %i: %.3f" % (years, captial))


def init():
    print()
    print('''The following are the available services:
1. Query assets
2. Deposit
3. Withdraw
4. Calculate compound interest
5. Calculate loan
6. Calculate future assets
q. Exit''')


def main():
    init()
    while True:
        choice = input("Please enter the service code you want to use: ")
        # Query balance
        if choice == "1":
            balance()
        # Deposit
        elif choice == "2":
            inc = float(input("Please enter deposit amount: "))
            saving(inc)
        # Withdrawal
        elif choice == "3":
            dec = float(input("Please enter withdrawal amount: "))
            draw_money(dec)
        # Calculate regular investment
        elif choice == "4":
            investment = float(input("Please enter the monthly regular investment amount: "))
            annual_rate = float(input("Please enter the annual return rate: "))
            years = int(input("Please enter the investment period (years): "))
            if investment <= 0 or annual_rate <= 0 or years <= 0:
                print("The input data is incorrect")
            else:
                money = fixed_investment(investment, annual_rate, years)
            print("Final gain: %.2f yuan" % money)
        # Calculate loan
        elif choice == "5":
            loan = float(input("Please enter current loan: "))
            rate = float(input("Please enter annual interest rate: "))
            pay = float(input("Please enter annual repayment: "))
            if loan <= 0 or rate <= 0 or pay <= 0:
                print("The input data is incorrect")
            else:
                loans(loan, rate, pay, 0)
        elif choice == "6":
            years = int(input("How many years later would you like to check the financial status? "))
            future(years)
        # Exit
        elif choice == "q":
            print("Welcome back next time! Goodbye!")
            break
        else:
            print("The command you entered is incorrect, please re-enter\n")


if __name__ == '__main__':
    main()