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Simple I/O problem can't get solved

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  Simple I/O problem can't get solved nickgan.sps@windowslive.com - 2013-06-21 01:57 -0700
    Re: Simple I/O problem can't get solved Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2013-06-21 12:11 +0300
    Re: Simple I/O problem can't get solved Peter Otten <__peter__@web.de> - 2013-06-21 11:15 +0200
      Re: Simple I/O problem can't get solved nickgan.sps@windowslive.com - 2013-06-21 02:20 -0700
    Re: Simple I/O problem can't get solved Chris Angelico <rosuav@gmail.com> - 2013-06-22 19:07 +1000
    Re: Simple I/O problem can't get solved Peter Otten <__peter__@web.de> - 2013-06-22 12:11 +0200
    Re: Simple I/O problem can't get solved Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-06-22 12:58 -0400

#48848 — Simple I/O problem can't get solved

Greetings to everybody,

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()
	if len(line) == 0:
		break
	elif is_palindrome.is_palindrome(line):	
		print line,
f.close()
***

I have coded the is_palindrome module before and it works very well.
Here is this module's code:

***
def reverse(text):
	return text[::-1]

def replace_all(text, dic):
	for i, j in dic.iteritems():
		text = text.replace(i, j)
	return text

def is_palindrome(text):
	return text == reverse(text)
	
points = {'.':'', ',':'', '!':'', ';':'', '?':'', '/':'', '\\':''}

something = raw_input('Enter text: ').lower().replace(' ', '')
replace = replace_all(something, points)
if is_palindrome(replace):
	print 'Yes, it is a palindrome:', reverse(replace)
else:
	print 'No, it is not a palindrome:', reverse(replace)
***

What should I do to output only the palindrome lines from the text file?

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#48850

nickgan.sps@windowslive.com writes:

> 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()
> 	if len(line) == 0:
> 		break
> 	elif is_palindrome.is_palindrome(line):	
> 		print line,
> f.close()

There's a newline at the end of each input line. Strip that. (It might
be another sequence that means end-of-line in your system. It can
still be stripped as trailing whitespace. Strings have a method for
stripping trailing whitespace.)

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#48851

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

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#48853

Τη Παρασκευή, 21 Ιουνίου 2013 12:15:59 μ.μ. UTC+3, ο χρήστης Peter Otten έγραψε:
> 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

Thank you a lot it worked!

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#48920

On Fri, Jun 21, 2013 at 7:15 PM, Peter Otten <__peter__@web.de> wrote:
> Combining these modifications:
>
> for line in f:
>     word = line.strip()
>     if is_palindrome.is_palindrome(word):
>         print word

Minor quibble: I wouldn't use the name 'word' here, unless you're
expecting the file to consist of one-word lines (such as DICTOT.DIC
from old PMMail). For detecting phrase/sentence palindromes, I'd keep
the name 'line'.

ChrisA

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#48921

Chris Angelico wrote:

> On Fri, Jun 21, 2013 at 7:15 PM, Peter Otten <__peter__@web.de> wrote:
>> Combining these modifications:
>>
>> for line in f:
>>     word = line.strip()
>>     if is_palindrome.is_palindrome(word):
>>         print word
> 
> Minor quibble: I wouldn't use the name 'word' here, unless you're
> expecting the file to consist of one-word lines (such as DICTOT.DIC
> from old PMMail). For detecting phrase/sentence palindromes, I'd keep
> the name 'line'.

Somehow it didn't occur to me that you might test anything but words.
However, if you want to check sentences (as some unused code in the original 
post suggests) I think you should not strip off the newline and leave the 
necessary cleanup to the test function:

>>> def is_palindrome(s):
...     t = "".join(c for c in s.casefold() if c.isalnum())
...     return t == t[::-1]
... 
>>> is_palindrome("A man, a plan, a canal - Panama!\n")
True

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#48935

On Sat, 22 Jun 2013 19:07:59 +1000, Chris Angelico <rosuav@gmail.com>
declaimed the following:

>On Fri, Jun 21, 2013 at 7:15 PM, Peter Otten <__peter__@web.de> wrote:
>> Combining these modifications:
>>
>> for line in f:
>>     word = line.strip()
>>     if is_palindrome.is_palindrome(word):
>>         print word
>
>Minor quibble: I wouldn't use the name 'word' here, unless you're
>expecting the file to consist of one-word lines (such as DICTOT.DIC
>from old PMMail). For detecting phrase/sentence palindromes, I'd keep
>the name 'line'.
>
	There's also the matter of whether one is looking for strict
palindromes -- where spacing is included (but not letter case)

Able was I ere I saw Elba

or a looser definition where only the letters are involved in the
determination (again ignore case and punctuation, but also ignore the
spaces between words)

Madam I'm Adam
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/

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