[Tutor] try except continue (fwd)

[Smith, Jeff]

The problem with the original solutions is that strings are immutable so

if not line.strip():
	continue

doesn't actually remote the new line from the end so when you do

print line

you get two new lines: one from the original and one from the print
command.  You either need

import sys
for line in sys.stdin:
  if not line.strip():
    continue
  print line, #<-- note the comma

or my preference

import sys
for line in sys.stdin:
  line = line.strip()
  if not line:
    continue
  print line

Jeff


-----Original Message-----
From: Danny Yoo [mailto:dyoo at hkn.eecs.berkeley.edu] 
Sent: Wednesday, August 24, 2005 2:29 PM
To: Tutor
Subject: Re: [Tutor] try except continue (fwd)




---------- Forwarded message ----------
Date: Wed, 24 Aug 2005 11:24:44 -0700
From: tpc247 at gmail.com
Reply-To: tpc at csua.berkeley.edu
To: Danny Yoo <dyoo at hkn.eecs.berkeley.edu>
Subject: Re: [Tutor] try except continue

hi Danny, I finally had a chance to review your explanation of continue
you wrote a while back, and I think I understand it.  You say the
program will filter empty lines from standard input.  I expected the
behavior to be such that, upon running the program, and typing:

hello

Danny

and pressing ctrl-d, I would get:

hello
Danny

Instead, I got the former output, which surprised me.  Why doesn't your
program work as I expected ?  I then wondered what your program would do
if I slightly modified it.  *grin*

import sys

for line in sys.stdin:
    print line

This time, running the same former test, I got the following output:

hello



Danny

As you can see, there are three empty lines now, not just one !  Where
did the extra empty lines come from ?

On 7/28/05, Danny Yoo <dyoo at hkn.eecs.berkeley.edu> wrote:
>
>
> Hi Tpc,
>
> I should have written an example of 'continue' usage to make things 
> more explicit.  Here is a simple example:
>
> ###
> """Filters empty lines out of standard input."""
> import sys
> for line in sys.stdin:
>     if not line.strip():
>         continue
>     print line
> ######
>
> This is a small program that filters out empty lines from standard 
> input. The 'continue' statement causes us to immediately jump back to 
> the beginning of the loop and to keep going.
>
>
>
>
> In Python, continue is intrinstically tied with Python's looping 
> operations (while/for).
>
>     http://www.python.org/doc/ref/continue.html
>
> It has very little to do with exception handling, except where the 
> footnotes mentions certain artificial limitations in using it within 
> an exception-handling block.
>
>

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