Why is my conditional returning "none?"

Question

Whenever I run this I get the third option when it should be returning the first, since s = 'yes'. What is going wrong here?

def shut_down(s):
    if s is 'yes':
        return 'Shutting down...'
    elif s is 'no':
        return 'Shutdown aborted!'
    else:
        return "Sorry, I didn't understand you"

ans = 'Yes'
s = ans.lower()
shut_down(s)

This is a repeat of http://stackoverflow.com/questions/2988017/string-comparison-in-python-is-vs — Daniel Williams, Mar 16 '13 at 22:55

score 5 · Answer 1 · answered Mar 16 '13 at 22:55

5

Change

if s is 'yes':

to

if s == 'yes':

and

elif s is 'no':

to

elif s == 'no':

While is is a valid operator, it is not the one to use here (it compares object identity instead of comparing the character sequences).

answered Mar 16 '13 at 22:55

NPE

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score 4 · Answer 2 · answered Mar 16 '13 at 22:55

4

is tests for identity, not equality. To test if a string is equal to yes use s=='yes'

answered Mar 16 '13 at 22:55

Ivaylo Strandjev

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Why is my conditional returning "none?"

2 Answers2