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To: python-list@python.org
From: Peter Otten <__peter__@web.de>
Subject: Re: Simple I/O problem can't get solved
Date: Fri, 21 Jun 2013 11:15:59 +0200
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nickgan.sps@windowslive.com wrote:

> I have recently started to solve my first Python problems but I came
> across to this:
> Write a version of a palindrome recogniser that accepts a file name from
> the user, reads each line, and prints the line to the screen if it is a
> palindrome.(by http://www.ling.gu.se/~lager/python_exercises.html)
> 
> I think I coded it correctly but still I get no output. I do not have any
> errors I just do not get any output.
> 
> This is the code:

> import is_palindrome
> 
> filename = raw_input('Enter a file: ') # A text file
> f = open(filename)
> while True:
>         line = f.readline()

The line includes the trailing newline character which breaks the symmetry:

>>> "abba" == "abba"[::-1]
True
>>> "abba\n" == "abba\n"[::-1]
False

Use

word = line.strip()

to remove all leading and trailing whitespace.

>         if len(line) == 0:
>                 break
>         elif is_palindrome.is_palindrome(line): 
>                 print line,
> f.close()

Note that python allows you to iterate over the lines of a file with

for line in f:
    ...

Combining these modifications:

for line in f:
    word = line.strip()
    if is_palindrome.is_palindrome(word):
        print word