[Python-Dev] RE: PEP-317

[sismex01@hebmex.com]

> From: Aahz [mailto:aahz@pythoncraft.com]
> Sent: Tuesday, June 10, 2003 9:23 AM
> 
> Yeah.  I've been thinking a bit, and while the proposed change makes
> some sense for the case where you're passing an argument to an
> exception, it makes this look uglier:
> 
> class Found(Exception):
>     pass
> 
> try:
>     for record in records:
>         for field in record.fields:
>             if data in field.data:
>                 raise Found()
> except Found:
>     # handle success
> else:
>     # handle failure
> 
> I find that extra set of parentheses unnecessary and ugly.  
> It implies a callable where it's not really being used that
> way, particularly in the asymmetry between the ``raise`` and
> the ``except``.
>

On the other hand, I read it quite clear; the extra set
of parenthesis you find so ugly, imply to me that an
instance of Found is being raised, and that except: is
going to catch all instances of Found.  It's a matter
of taste, that you (aesthetically) like it or not,
but it's a matter of consistency and correctness that
it should be there or not.

>
> If this change goes through, I might start doing
> 
> class Found(Exception):
>     pass
> Found = Found()
>

You won't catch anything in that case, check this out:

Python 2.2 (#28, Dec 21 2001, 12:21:22) [MSC 32 bit (Intel)] on win32
Type "copyright", "credits" or "license" for more information.
IDLE 0.8 -- press F1 for help

>>> class Found(Exception):
	pass

>>> Found = Found()
>>> def fnEx():
	try:
		print "Fire in the hole!"
		raise Found
	except Found:
		print "Fire extinguished."

		
>>> 
>>> 
>>> fnEx()
Fire in the hole!
Traceback (most recent call last):
  File "<pyshell#21>", line 1, in ?
    fnEx()
  File "<pyshell#18>", line 4, in fnEx
    raise Found
Found
>>> 
>>> isinstance(Found,Found)
Traceback (most recent call last):
  File "<pyshell#22>", line 1, in ?
    isinstance(Found,Found)
TypeError: isinstance() arg 2 must be a class or type
>>> 


You can't catch instances of the Found.__class__
by referring to Found, you'd have to do something
like this:


>>> 
>>> def fnEx():
	try:
		print "Fire in the hole!"
		raise Found
	except Found.__class__:
		print "Caught."

		
>>> 
>>> fnEx()
Fire in the hole!
Caught.
>>> 


There it did get caught, but it seems quite uglier
than an extra pair of parenthesis.

just my 2 cents.

-gca

pd: Please excuse this unnecessary, hideous and wasteful
    legalese. :-(
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