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[Python-ideas] except expression

Chris Angelico rosuav at gmail.com
Tue Feb 18 17:06:15 CET 2014 
On Wed, Feb 19, 2014 at 2:56 AM, Paul Moore <p.f.moore at gmail.com> wrote:
> On 18 February 2014 15:05, Chris Angelico <rosuav at gmail.com> wrote:
>>> Well, yes and no. There are only 2 out of the 10 syntaxes originally
>>> proposed in the PEP at the start of this thread that use a colon. I've
>>> already pointed out that I don't like a colon, so assume I said
>>> "except return 0" if you must :-)
>>
>> Whether it's a colon or another keyword, _something_ is necessary in
>> there, if it's permissible to specify an exception type:
>>
>> sum(x[3] except IndexError 0 for x in list_of_tuples)
>> sum(x[3] except 0 for x in list_of_tuples)
>>
>> How would you parse each of those, without a separator?
>
> With "return" as a separator. I said that above. Was I not clear?

Sure. Sorry, got a bit of brain-fry at the moment; misinterpreted your
last sentence three chevrons in. So yeah, that would be:

sum(x[3] except IndexError return 0 for x in list_of_tuples)
sum(x[3] except return 0 for x in list_of_tuples)

> I remain less than happy with the colon notation, although I will
> concede that the basic
>
>     x[3] except IndexError: 0
>
> form is not horrible - it just becomes horrible very, very fast when
> people try to do anything more complicated than that. On the other
> hand, none of the examples of *any* of the proposed syntaxes look
> compelling to me - they are either too simple to be realistic, or so
> complex that they should be factored out into multiple statements, in
> my view.

The same can be said for if/else and the short-circuiting uses of
and/or, both of which have wide-spread support, and not just from
folks like me who grew up with C.

I'm currently working on finding a bunch of examples from the stdlib
that could be translated. Will post them once I get the script sorted
out. As it's currently 3AM, though, that means I need to fry up some
bacon or something before I continue :)

ChrisA
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