计算器中的运算符无效

如何解决计算器中的运算符无效

我是编程新手，想利用迄今为止所获得的知识制作自己的计算器。 出于某种原因，它告诉我我的第一个运算符无效。有人能告诉我我做错了什么吗？也许我还需要修复什么？不要在我的计算器上加任何东西，我想自己做。谢谢。

num1 = float(input("Enter first number: "))
op = input("Enter operator: ")

if op != ("+","-","/","*","%"):
    print("Invalid operator.")
    exit()

num2 = float(input("Enter second number: "))

yesno = input("More numbers? ")

if yesno == ("Yes","yes","Y","y"):
    op2 = input("Enter second operator: ")
    num3 = float(input("Enter another number: "))
elif yesno == ("No","no","N","n"):
    pass
else:
    print("Invalid answer.")

    if op and op2 == "":
        print(num1 + op + num2)
    elif op and op2:
        print(num1 + op + num2 + op2 + num3)