why does python tell me that my yes variable not defined?

Question

I wrote this script with Python 2.7:

name=raw_input("Hi im a PC, who are you?")

print("Hi " + name + " how are you, are you good?")

answer = raw_input("")

if (answer) == yes:
    print("That's good to hear")
elif (answer) == no:
    print("Oh well")
else:
    print("Sorry, you didnt answer the question properly, Please answer with a yes or no")

This is the error I get:

Traceback (most recent call last):

File "C:/Python27/programs/2", line 4, in 

     if (answer) == yes:

NameError: name 'yes' is not defined

Answer 1

you have no variable named yes ,
What you are trying to do is compare the user input to the string "yes"

which would go like:

if answer == "yes":
    # do stuff

There is also no need for those brackets around answer.

Answer 2

answer是一个字符串，您应该使用answer == "yes"

Answer 3

You need to put " or ' in your strings. yes is not "yes" , and no is not "no" .

#if (answer) == yes:
if (answer) == "yes":

#elif (answer) == no:
elif (answer) == "no":

The error name 'yes' is not defined is because the interpreter looked for a variable called yes because the word is without " or ' . If you write "yes" the interpreter will compare the value of answer variable with the string "yes" .