[Python-ideas] except expression

[Rob Cliffe]

On 19/02/2014 01:40, Jan Kaliszewski wrote:
> 19.02.2014 02:11, Chris Angelico wrote:
>
>> On Wed, Feb 19, 2014 at 11:19 AM, Jan Kaliszewski <zuo at chopin.edu.pl> 
>> wrote:
>>> 18.02.2014 17:25, Paul Moore napisał:
>>>
>>>
>>>> OTOH, there's still an argument for only allowing a single exception
>>>> name in the syntax (an "identifier" rather than an "expression" in
>>>> syntax terms). If you must catch multiple exceptions, give the
>>>> relevant tuple a name.
>>>
>>>
>>> I believe that at this point (what the exception spec would be
>>> allowed to be: identifier?, tuple?, any expression?) the syntax should
>>> be identical to the statement syntax (i.e.: any expression).
>>>
>>> Less special cases to remember.
>>
>> Yes, definitely. I see little value in forcing single-exception 
>> catching.
Uh yes.  I thought/hoped the debate had got past this point.
>>
>>> For the same reason, I believe that tuple expressions
>>> ("except (ValueError, TypeError)") should be obligatorily
>>> enclosed with parens as long as they are obligatorily enclosed
>>> with parens in the statement syntax (i.e., probably till Python 3.13
>>> :)).
>>
I think I agree on grounds of (sorry if I'm becoming a bore, but you 
guessed it!) Consistency!  But I don't see this as a critical issue, 
particularly as Python 3.13 is probably a few weeks away :-) .  I think 
putting parens around a list of exceptions would be good style in any case.
Rob Cliffe
>> AFAIK, the only reason to mandate the parens is to specifically
>> disallow the Py2 syntax:
>>
>> except Exception, e:
>>     pass
>>
>> If that's the case, they could be optional in the expression form, as
>> that has no Py2 equivalent.
>
> But then you must remember: in expression yes, in statement no;
> + additional trouble when you refactor transforming the former to
> the latter...
>
> Cheers.
> *j
>
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