为什么它说响应没有定义，即使它是

Question

It keeps telling me response is not defined.

while response not in Yes or No:
    response = input("Would you like to shut down the program?\nyes/no\n")
if response == "Yes":
    print("Goodbye.\n")
elif response == "No":
    print("Ok.")
    quit()
else: 
    print("I didn't understand that.\n")

Answer 1

Assuming it's not referenced above the code you provide, the first time through the loop, response is not defined. Only after the first call to input() . You need to initialize before the loop. Something like response = None should suffice.

Answer 2

Since Python is case sensative, converted response to upper case.

response.upper() == "YES":

response.upper() == "No":

response = input("Would you like to shut down the program?\nyes/no\n") 
if response.upper() == "YES":
     print("Goodbye.\n") 
elif response.upper() == "NO": 
     print("Ok.") 
     #quit() 
else: 
     print("I didn't understand that.\n")