palindrome iteration

Peter Otten __peter__ at
Fri Aug 27 11:33:15 CEST 2010

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

Do yourself a favour and use 4-space indent. That makes the structure of 
your code more obvious.
> print i_palindrome('annab')
> my reasoning:
> - i check the length of the string: if > 1 continue
> - i check first and last char: if they are equal continue
> - create a new, shorter string starting at index 1 and ending at
> second last index (up to but not including index-1
> -restart the while loop as long as length of string is > 1
> - exiting this loop means all compared chars were identical hence it
> is a palindrome and i return True

If the test pal[0] == pal[-1] fails, i. e. the two compared characters 
differ, what happens?

More generally, if pal is not a palindrome, can your function ever return 
False? If not, at what point should it?


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