Python Recursive Function to Check if Palindrome

Question

I need to define a recursive function to check if a string is a palindrome.

Below's my code:

def palindrome_recur(string):

    if len(string)==0 or 1:
        return True
    else:
        if string[0] == string[-1]:
            return palindrome_recur(string[1:-2])
        else:
            return False

It passes a few test cases, but doesn't work for the string "chipmunks". Can anybody tell me what I might have overlooked?

@MartijnPieters hardly, the OP didn't know that was the problem, and also there is another issue with the slicing of couse. — anon582847382, Apr 14 '14 at 10:19
@AlexThornton: that's a small issue that could be addressed in a comment; the main issue here is the misunderstanding how `or` works. And that's exactly what the dupe addresses. — Martijn Pieters, Apr 14 '14 at 10:21
ahh, thank you so much everyone! still a beginner at programming! thank you — user3531425, Apr 14 '14 at 12:54
I think line #7 should be `return palindrome_recur(string[1:-1]) — jayko03, Jun 16 '17 at 19:15

sshashank124 · Answer 1 · 2014-04-14T10:01:02.177

1

You should pass the recursive call as: return palindrome_recur(string[1:-1]) instead.

Also, your len check is not correct. Do this instead:

if len(strg)==0 or len(strg)==1:

edited Apr 14 '14 at 10:01

answered Apr 14 '14 at 09:55

sshashank124

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score 1 · Accepted Answer · answered Apr 14 '14 at 09:59

1

The problem is this:

if len(string)==0 or 1:

That checks whether either of len(string) == 0, or 1 is true. Since 1 is always true, the whole expression is always true and your function always returns True.

You should use

if len(string) <= 1:

instead.

Then, you'll find out about the problem with indexing to -2 that the other answers mention.

answered Apr 14 '14 at 09:59

RemcoGerlich

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Thank you for the explanation! I'm still a beginner at programming. Guess I missed out on that bit! – user3531425 Apr 14 '14 at 12:54

Python Recursive Function to Check if Palindrome

2 Answers2