exception arg

[Paul Robinson]

Mirko Nasato wrote:
> 
> I can't understand the following:
> 
> >>> 1/0
> Traceback (innermost last):
>   File "<stdin>", line 1, in ?
> ZeroDivisionError: integer division or modulo
> >>> try:
> ...     1/0
> ... except ZeroDivisionError, arg:
> ...     if arg == "integer division or modulo":
> ...             print "This is what I expect."
> ...     else:
> ...             print 'Unexpected. "arg" is "%s".' % arg
> ...
> Unexpected. "arg" is "integer division or modulo".
> >>>
> 
> The same seems to occur with every kind of exception, so maybe
> there's an explanation...

There is: arg is not a string....

For example:
PythonWin 1.5.2 (#0, Apr 13 1999, 10:51:12) [MSC 32 bit (Intel)] on
win32
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
Portions Copyright 1994-1999 Mark Hammond (MHammond at skippinet.com.au)
>>> try:
... 	1/0
... except ZeroDivisionError, arg:
... 	print type(arg)
...     print `arg`
...     print arg
...     print str(arg) == 'integer division or modulo'
... 	
<type 'instance'>
<exceptions.ZeroDivisionError instance at 1137370>
integer division or modulo
1
>>> 

arg is an instance of an exception object.

The string that you were comparing it with is the string representation
of that object.

Hope that helps,
	Paul.