Python: MathBot

commands = ["add","subtract","multiply","divide","power"]
operators = ["+","-","*","/","**"]

def mathquestion():
    instruction = input("What maths function would you like to perform? ").lower()
    operator = operators[commands.index(instruction)]
    first = int(input("Please type your first number: "))
    second = int(input("Please type your second number: "))
    expression = str(first)+operator+str(second)
    result = eval(expression)
    print(expression+" = "+str(result))

finished = False
while not finished:
    mathquestion()
    another = input("Another question? ")
    if another.lower()[0:1]=="n":
        finished = True
print("OK, bye!")