tip2.py

import sys

def main():
    subtotal = float(input('How much was the bill? '))
    service = input('How was the service?  (b)ad/(a)vg/(g)ood: ')
    t = calcTotal(subtotal,service)
    print(f'The bill is ${t:.2f}.  Thank you!')

def calcTotal(st, svc):
    if svc == 'b':
        tip = .02
    elif svc == 'a':
        tip = .20
    elif svc == 'g':
        tip = .30
    else:
        print('Invalid option')
        sys.exit(1)

    total = st * (1+tip)
    return total

main()