Pythonic exceptionalism (was: A C-like if statement)

[Cameron Laird]

In article <pan.2006.02.23.22.14.53.56541 at REMOVETHIScyber.com.au>,
Steven D'Aprano  <steve at REMOVETHIScyber.com.au> wrote:
>On Thu, 23 Feb 2006 12:04:38 -0700, Bob Greschke wrote:
>
>>> try:
>>>    i = a.find("3")
>>>    print "It's here: ", i
>>> except NotFound:
>>>    print "No 3's here"
>> 
>> Nuts.  I guess you're right.  It wouldn't be proper.  Things are added or 
>> proposed every day for Python that I can't even pronounce, but a simple 'if 
>> (I = a.find("3")) != -1' isn't allowed.  Huh.  It might be time to go back 
>> to BASIC. :)
>
>There are *reasons* why Python discourages functions with side-effects.
>Side-effects make your code hard to test and harder to debug.
>
>> I think your way would work if .find() were replaced with .index().  I'm 
>> just trying to clean up an if/elif tree a bit, so using try would make 
>> things bigger.
>
>Then write a function! Instead of calling the try..except block in every
>branch directly, pull it out into a function:
>
>def test(s,what):
>    try:
>        i = s.index(what)
>        print "It's here: ", i
>    except ValueError:
>        print "No 3's here"
			.
			.
			.
A recent piece by Collin Park <URL:
http://www.linuxjournal.com/article/8794 >
illustrates how a user-defined exception
arises so naturally in a tiny toy example
that it occurs to a teenager first program-
ming.