为什么我的项目不允许用户退出程序?

你有一些语法错误，但主要的问题是退出调用

input_exit = input('Press 0 to exit the program: ')
if input_exit == '0':
    print('Thank you for choosing Lit Rentals')
    exit(0)
elif input_exit == '1':
    getInput()

关于你的更新:

from decimal import Decimal

def charge_calc(slot, days_rented, miles_driven, baseChargeDaily, baseChargeWeekly, MileageCharge):
        w, d = divmod(days_rented, 7)
        total_charge = d *baseChargeDaily[slot]
        total_charge += w *baseChargeWeekly [slot]
        if w > 0:
            miles_driven = miles_driven -200
        total_charge = total_charge + miles_driven * MileageCharge [slot]
        return total_charge

def application_flow():
    print(" ______________________________________________")
    print("|                                              |")
    print("|              <3   Lit Rentals    <3          |")
    print("|    Update: Class A, B, and C are availble    |")
    print("|                  Instructions                |")
    print("|   1.) Enter your full name (no numbers!)     |")
    print("|   2.) Enter the Truck class you like to rent |")
    print("|   3.) Enter the days you have rented for ONLY|")
    print("|   4.) Enter your starting mileage (NUMBERS!) |")
    print("|   5.) Enter your ending mileage (NUMBERS!)   |")
    print("|   6.) Review your bill and enter 0 when done |")
    print("|   7.) If not done or wanting to start the    |")
    print("|   program again with the number 1            |")
    print("|______________________________________________|")

    enterName = (input('Please enter your full name: ')).upper()
    try:
        classCode = (input('Please enter your rental classification code (Class A, Class B, Class C): ')).upper()
    except:
        print("Please enter the correct letter and try again")
        classCode = (input('Please enter your rental classification code (Class A, Class B, Class C): ')).upper()
    try:
        days_rented = int(input('How many days did you rent your vehicle for? '))
    except:
        print("Error! You enterted the wrong input, please give a number.")
        days_rented = int(input('How many days did you rent your vehicle for? '))
    try:
        initOdometer = int(input('What was your vehicle\'s initial odometer reading (in Miles)? '))
    except:
        print("Error! Please neter the correct number for mileage and try again.")
        initOdometer = int(input('What was your vehicle\'s initial odometer reading (in Miles)? '))
    try:
        finOdometer = int(input('What was your vehicle\'s final odometer reading (in Miles)? '))
    except:
        print("Error! Please enter the final mileage in numbers and try again.")
        finOdometer = int(input('What was your vehicle\'s final odometer reading (in Miles)? '))
    # Final odometer reading
    # Formula for miles driven during rental period:

    miles_driven = finOdometer - initOdometer

    # Calculations based on the three possible class codes:

    classifications = ['A','B','C']
    baseChargeDaily = [Decimal('17.95'), Decimal('27.95'), Decimal('37.95')]
    baseChargeWeekly = [Decimal('107.59'), Decimal('166.59'), Decimal('237.99')]
    MileageCharge = [Decimal('0.49'), Decimal('0.69'), Decimal('0.79')]
    slot = 0

    if classCode == 'A': 
        slot = 0

    elif classCode == 'B': 
        slot = 1

    elif classCode == 'C': 
        slot = 2

    # call the function and assign the returned values
    final_bill= charge_calc(slot, days_rented, miles_driven, baseChargeDaily, baseChargeWeekly, MileageCharge)

    # Code for final output statements:
    if classCode == 'A' or classCode == 'B' or classCode == 'C':
        print('\nSummary:')
        print()
        print('Name of vehicle enter: %s' % enterName)
        print('Number of days vehicle rented: {}'.format(days_rented))
        print('Initial odometer reading on rented vehicle: {} miles'.format(initOdometer))
        print('Final odometer reading on rented vehicle: {} miles'.format(finOdometer))
        print('Number of miles driven during rental period: %d' % (miles_driven))
        print('\n Final billing cost: $%.2f' % final_bill)

    input_exit = input('Press 0 to exit the program or 1 to restart: ')
    if input_exit == '0':
        print('Thank you for choosing Lit Rentals')
        exit(0)
    elif input_exit == '1':
        application_flow()

application_flow()

getInput不是一个预定义的方法。在这种情况下，如果希望能够“重新启动”程序流，则需要理解重新启动的含义。在本例中，您希望允许用户再次插入数据。因此，实现此目的的一种方法是将所需的流封装到一个方法中，并在希望重新启动它时简单地调用它。