[Tutor] do: vs. while: (was: deleting CR within files)

[Roger Merchberger]

Rumor has it that Alan Gauld may have mentioned these words:

[[[ Dudez... I'm on the list, and I hopped out of this thread quite a while 
ago... ;-) ]]]

>>Is there such a thing as a do loop in Python?
>
>There's a while loop which will do anything a do loop can,
>but...

Not quite. IIRC, in VB and some other basics, there are both do/until 
loops, and while/wend loops. The difference is this:

while/wend loops are always evaluated at the beginning of the loop and run 
the "risk" of not get executing at all if the initial test is false; try this:

while 0:
   print "You will never see this."

whereas do/until loops are evaluated at the end and always execute, at 
least once, in pythonlike-parlance, it would look like this:

do:
   print "you will see this anyway, even tho the test is false..."
   until 0   # Yes, I know this isn't python... it's an example, eh?

As previously posted, if you *gotta have* the do/until functionality, just 
use a while 1: loop, and put your test at the bottom of the loop with a 
breakout, like this:

while 1:
   print "You will see this once; maybe more depending on the test."
   if gitmeouttahere:
     break

IMNSHO, I always thought having both a do/until and while/wend loop 
structures were overkill, as it was so easy to replicate one with the other...

>>done.  In my program I have a simple widget and need to initiate it before
>>my dialog pops up.  And then give the user the option to select more files
>>with the same widget.
>
>I think you are missing the point of event driven programming.
>When they press the widget it processes a file, if they press
>it again it processes another file, and so on.
>
>In other words you don't need a loop to do that. Or more to
>the point the Tk.mainloop() is the only loop you need.
>
>>I know that I need to use some kind of loop and in VB
>>a do loop would work best.  But what about in Python?
>
>You shouldn't need a loop in VB either!

*unless* he's referencing a multi-selectable combo box - then you're both 
correct. He doesn't need a loop to work the main structure of the GUI, but 
he will need some form of loop to work each of the files that's been 
multi-selected.

Of course, that's the beauty of "for eachfile in mycombobox:" ;-)

As an aside, in VB, the "Tk.mainloop()" structure is implied - it's totally 
hidden from the user, so he may not understand why it's required in Python...

Anywho, HTH and HAND... ;-)
Roger "Merch" Merchberger

--
Roger "Merch" Merchberger   ---   sysadmin, Iceberg Computers
zmerch at 30below.com

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