Python

Odd- Length Palindrome

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Join Date: Oct 2009

Posts: 18

Reputation: pyprog is an unknown quantity at this point

Solved Threads: 0

pyprog

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Newbie Poster

Odd- Length Palindrome

Oct 24th, 2009

The following code should return the longest odd-length palindrome in a string centered at the index. So in a string 'asradarer' it should return 'radar'. Can you explain to me what the problem here is?

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def get_odd_palindrome_at(word, index):
    num = 1
    new_word = ""
    while index < len(word):
        if word[index - num] == word[index + num]:
            print new_word + word[index - num:index + (num + 1)]
        num += 1
   else:
          print ""
def get_odd_palindrome_at(word, index):
    num = 1
    new_word = ""
    while index < len(word):
        if word[index - num] == word[index + num]:
            print new_word + word[index - num:index + (num + 1)]
        num += 1
   else:
          print ""

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Join Date: Sep 2009

Posts: 112

Reputation: AutoPython is an unknown quantity at this point

Solved Threads: 9

AutoPython AutoPython is offline

Offline

Junior Poster

Oct 25th, 2009

Well, what's happening, what's going wrong with the program? Could you post the error message.

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Join Date: Jun 2008

Posts: 128

Reputation: slate is an unknown quantity at this point

Solved Threads: 31

slate

Offline

Junior Poster

Oct 25th, 2009

Your description is incorrect. This function will never return 'radar' on any string input, because it needs another parameter.

Your loop does not exit. You increment num, but the loop's exit expression does not depend on it.
It possibly exits on index error if num becomes too large. At first sight.

The code has indent error. The else row is loose.

The else clause is redundant without a break statement in the loop. Unless you use exceptions for something weird.

I suggest you read the problem you are solving once more. And do not forget to read your own posts before hitting the submit button.

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Join Date: Oct 2004

Posts: 4,113

Reputation: vegaseat is just really nice

Solved Threads: 944

vegaseat

Offline

DaniWeb's Hypocrite

Oct 25th, 2009

Your problem stems from the fact that you never give index an updated value in the while loop. I would use the while loop this way ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
def get_odd_palindrome_at(word, index):
    num = 1
    new_word = ""
    while True:
        if index + num > len(word) - 1:
            break
        if word[index - num] == word[index + num]:
            print new_word + word[index - num:index + (num + 1)]
        num += 1
    else:
        print ""
 
word = 'asradarer'
print len(word)  # test
index = len(word)//2 
get_odd_palindrome_at(word, index)
def get_odd_palindrome_at(word, index):
    num = 1
    new_word = ""
    while True:
        if index + num > len(word) - 1:
            break
        if word[index - num] == word[index + num]:
            print new_word + word[index - num:index + (num + 1)]
        num += 1
    else:
        print ""

word = 'asradarer'
print len(word)  # test
index = len(word)//2 
get_odd_palindrome_at(word, index)