[Python-ideas] (try-except) conditional expression similar to (if-else) conditional (PEP 308)

[Jae Kwon]

How about making this work?

foo = try: float(string) except SomethingError, e: float(NAN)

This would imply that try blocks have a value. Maybe even allow this:

foo = try:
     float(string)
except Something Error, e:
     float(NAN)

Sure, it introduces a couple new grammar tweaks, but it's easy to  
understand and is backwards compatible.

  - Jae


On Aug 7, 2009, at 12:21 AM, Mike Meyer wrote:

> On Fri, 07 Aug 2009 08:30:14 +0200
> Georg Brandl <g.brandl at gmx.net> wrote:
>
>> MRAB schrieb:
>>> Jan Kaliszewski wrote:
>>>>> Syntax Ideas:
>>>>>    Option 1:
>>>>>        x = float(string) except float('nan') if ValueError
>>>>>        op(float(string) except float('nan') if ValueError)
>>>>
>>>> -0.5
>>>> I wouldn't mix up 'if' word with 'except' -- there are different  
>>>> concepts.
>>>>
>>>>>    Option 2:
>>>>>        x = float(string) except ValueError: float('nan')
>>>>>        op(float(string) except ValueError: float('nan'))
>>>>
>>>> +0.5
>>>> IMHO seems to be the best of the propositions. I'd add to it  
>>>> optional
>>>> as (like in present 'try:... except Exc as exc:...')
>>>>
>>> Can there be multiple 'except's?
>>>
>>>     reciprocal = 1.0 / float(string) except ValueError: float('nan')
>>> except ZeroDivisionError: float('inf')
>>
>> Don't over-complicate.  This proposal has a slim chance of success  
>> as it
>> is; piling on top isn't going to help.
>
> Assuming you avoid the ':' version, shouldn't multiple excepts fall
> out of the grammar naturally?
>
> x = ((1.0 / float(string)
>      except float('nan') if ValueError)
>     except float('inf') if ZeroDivisionError)
>
> parses as "expr1 except float('inf') if ValueError", where expr1 is
> "(1.0 / float(string) except float('nan') if ValueError)".
>
> Yes, it's as ugly as nesting if/else expressions, but those work, so
> these should.
>
> FWIW, I'm +.5 on this. I don't see a lot of use for it, but can see
> that where it is useful, it's easier to read than a try:/except:.
>
>     <mike
> -- 
> Mike Meyer <mwm at mired.org>		http://www.mired.org/consulting.html
> Independent Network/Unix/Perforce consultant, email for more  
> information.
>
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