exception handling

[Mage]

Hello,


def error_msg(msg):
sys.exit(msg)

try:
do_something()
if value != my_wish:
error_msg('Inva lid input')
except:
print "Fatal IO or Network error"

This doesn't work because sys.exit raises an exception.

I know that I can define exception types after except, but there might
be many. Also I know I can write:
except:
if str(sys.exc_inf o()[0]) == 'exceptions.Sys temExit':
raise

But honestly I would like simething like that:

except (!SystemExit):

Is this possible somehow?

Mage

[Peter Otten]

Re: exception handling

Mage wrote:
[color=blue]
> def error_msg(msg):
> sys.exit(msg)
>
> try:
> do_something()
> if value != my_wish:
> error_msg('Inva lid input')
> except:
> print "Fatal IO or Network error"
>
> This doesn't work because sys.exit raises an exception.
>
> I know that I can define exception types after except, but there might
> be many. Also I know I can write:
> except:
> if str(sys.exc_inf o()[0]) == 'exceptions.Sys temExit':
> raise
>
> But honestly I would like simething like that:
>
> except (!SystemExit):
>
> Is this possible somehow?[/color]

try:
# may raise any exception
except SystemExit:
raise # propagate SystemExit (and subclasses)
except:
# handle everything else

Peter

[Roy Smith]

Re: exception handling

Mage <mage@mage.hu > wrote:
[color=blue]
> Hello,
>
>
> def error_msg(msg):
> sys.exit(msg)
>
> try:
> do_something()
> if value != my_wish:
> error_msg('Inva lid input')
> except:
> print "Fatal IO or Network error"
>
> This doesn't work because sys.exit raises an exception.[/color]

Peter Otten posted a good way to do what you want, but I'm not convinced
that it's a good idea.

You're assuming that any exception you get will be a "Fatal IO or Network
error". What if it's not? What if do_something() raises FutureWarning, or
KeyboardInterru pt, or AssertionError, or DeprecationWarn ing, or anything
else which has nothing to do with IO or networks? You would just end up
producing a misleading error message.

If you expect do_something() will throw certain exceptions, catch them
specifically. It's usually a mistake to catch everything. It's certainly
a mistake to catch everything and assume you know what it must be.

Try running the following code and see what happens:

import traceback

def do_something():
pass

try:
do_something()
if value != my_wish:
error_msg('Inva lid input')
except:
print "Fatal IO or Network error"
print traceback.print _exc()