Newbie looking for feedback

[Alex Martelli]

"Tyler Eaves" <tyler at tylereaves.com> wrote in message
news:39c1aa1e.6407246 at news.geeksnet.com...
> On Fri, 15 Sep 2000 04:43:52 GMT, David Lees
> <debl.spamnono at world.std.com> wrote:
>
> Still sorta a newbie myself, but here's my take.
>
> in=open('C:\\foo.txt','r').readlines()
> #Opens the input file and reads each line into a list entry
> out=open('C:\\bar.txt','w')
> #Open output file
> for x in in[:]:
> #Loop once for every line
> if len(x)>1:
> #Test to see if the line has anything....
> out.write(x)
> #It does! Write it!
>
> #Done!
> (5 lines of active code that gets the job done!)

Excellent -- except that it shouldn't work as written, because
"in" is a reserved word.  Still, it's easy to fix, with a few
nice little touches:

out = open(r'C:\bar.txt', 'w')
for line in open(r'c:\foo.txt').readlines():
    if len(line)>1:
        out.write(line)
out.close()

Notes:
    we can use the r'string' notation to let backslashes (\) be
    used in a platform-natural way on Windows, without doubling
    them up (we could also write 'c:/foo.txt', etc);

    we don't need an explicitly named object for the input-file,
    as we just get its list-of-lines in the for statement itself;
    thus, we don't need to close it, either (it is automatically
    closed by the Python runtime as soon as possible & convenient).

> >Two questions.  First, I have written a real simple Python routine to
> >remove blank lines from a text file.  The code below works but...
> >
> >1. I am sure this can be written much more simply, any hints?

See above: exploit the "for line in ...readlines()" idiom, use
the simplest of equivalent tests, here len(line)>1 rather than
line[0]!='\n' (not much of a difference, but some), use either
r'...' or /-notation for Windows filenames.  The first of these
is the one that makes a real difference, but the other may be
nice little touches of readability/simplicity.


> >2. Could someone point me to documentation or tell me how to use IDLE
> >under Windows to single step through the code.  It was a pain debugging
> >by executing the whole script as a run module command to IDLE.

(At least in IDLE 0.6, coming with the current 2.0b1 of Python; I
don't recall previous versions very well, particularly since I had
been using mostly PythonWin of late...): from main menu Debug, pick
the Debugger menuitem.  You'll see 4 checkboxes for what you'll want
to look at (stack, source, locals, globals) -- pick them appropriately --
and 5 buttons (Go/Step/Over/Out/Quit) currently disabled as nothing
is loaded.  Now from the interactive IDLE Python shell,
    import mymodule
will load your mymodule.py script and let you interact with it
through the debugger.


Alex