palindrome iteration

[Ian]

  On 27/08/2010 09:53, Baba wrote:
> level: beginner
>
> the following code looks ok to me but it doesn't work. I would like
> some hints as to where my reasoning / thought goes wrong
>
> def i_palindrome(pal):
>   while len(pal)>1:
>    if pal[0] == pal[-1]:
>     pal=pal[1:-1]
>   return True
>
> print i_palindrome('annab')
>
If you want to or must  do it recursively.
(Shown in pseudo code to make the logic clearer)

def isPalindrome(pal)
     ''' test pal (a list) is a palindrome '''
     if length of pal = 1
         return True # all one letter strings are palindromes.
     if first equals last
         # pal could be a palindrome
         #  so test inner part
         p = pal with first and last removed
         return  isPalendrome(p)   #  and true - implied
     else
         return False # it can't be

Of course, the simpler way is to use the definition of a Palindrome as 
the same backwards and forwards.

def isPalindrome(pal)
     return pal == pal.reverse