Python. Making a function that tests if a word is a palindrome recursively

Question

I'm trying to make a program that tests if a word is a palindrome using a recursive function. I pretty much have it working but I'm just having trouble with getting it to move on to the next letter if the first and last are the same.

word = input("enterword")
word = word.lower()

def palindrom(word):
    if len(word) == 1 or len(word) == 0:
        return 0;
    if word[0] == word[-1]:
        print(word[0], word[-1])
        palindrom(word);
    else:
        return 1;

test = palindrom(word)
if test == 0:
    print("Yes")
elif test == 1:
    print("No")

So right now it tests if the first and last letter are the same and if so, should run the function again. I just need to have it then check word[1] and word[-2] but I'm having some trouble. I tried splitting word and just popping the letters but it kept looking at the list as a length of 1. So if there is a way to get it to get the length of the whole split list, that would work as well.

Awww, come on. There are dozens of questions about the exact same topic: http://stackoverflow.com/questions/952110/recursive-function-palindrome-in-python?rq=1 http://stackoverflow.com/questions/4666339/python-and-palindromes?rq=1 http://stackoverflow.com/questions/8769890/performance-of-various-methods-to-test-for-a-palindrome-python?rq=1 — tamasgal, Mar 16 '15 at 20:41

Celeo · Accepted Answer · 2015-03-16T20:39:52.970

4

You're just missing the return statement when you call your method recursively and the correct slice:

def palindrom(word):
    if len(word) == 1 or len(word) == 0:
        return 0
    if word[0] == word[-1]:
        print(word[0], word[-1])
        return palindrom(word[1:-1])
    else:
        return 1

edited Mar 16 '15 at 20:39

answered Mar 16 '15 at 20:31

Celeo

5,583
8
39
41

Just to confirm. Does word[1:-1] increment it by that each time rather than telling it what position to read? – user3769402 Mar 16 '15 at 20:36
`word[1:-1]` returns the section of the word from position 1 to the penultimate letter. I.e. "*racecar*" becomes "*aceca*." – Celeo Mar 16 '15 at 20:37
See [this answer](http://stackoverflow.com/a/509295/2676531) for a good explanation. – Celeo Mar 16 '15 at 20:38
Ohh duh. Now I see it. Thanks. – user3769402 Mar 16 '15 at 20:38

score 0 · Answer 2 · answered Mar 16 '15 at 20:37

You are missing return statement, also you need to pass reduced word palindrom(word[1:-1]) on each recursion.

word = "viooiv"
word = word.lower()


def palindrom(word):
    if len(word) == 1 or len(word) == 0:
        return 0 
    if word[0] == word[-1]:
        print(word[0], word[-1])
        return palindrom(word[1:-1])
    else:
       return 1 

test = palindrom(word)
if test == 0:
    print("Yes")
elif test == 1:
    print("No"

Output:

 ('v', 'v')
 ('i', 'i')
 ('o', 'o')
 Yes

score 0 · Answer 3 · answered Mar 16 '15 at 20:43

0

Try calling palindrome on the word with this function:

def palindrome(word, i = 0):
    if i == len(word):
        return word[0] == word[-1]

    if word[i] == word[-i - 1]:
        return palindrome(word, i + 1)

    else:
        return False

answered Mar 16 '15 at 20:43

Malik Brahimi

16,341
7
39
70

Naveen Goyal · Answer 4 · 2020-07-12T07:29:15.917

0

A bit more shorter code:

def checkpalindrome(value):
    valuelen = len(value)
    if valuelen < 2:
        print("palindrome")
    else:
        checkpalindrome(value[1:valuelen-1]) if value[0] == value[-1] else print('Not palindrome')

edited Jul 12 '20 at 07:29

answered Jul 12 '20 at 07:20

Naveen Goyal

93
1
1
6

Python. Making a function that tests if a word is a palindrome recursively

4 Answers4