[Python-ideas] except expression

[Chris Angelico]

On Wed, Feb 19, 2014 at 12:00 AM, Paul Moore <p.f.moore at gmail.com> wrote:
> On 18 February 2014 12:49, MRAB <python at mrabarnett.plus.com> wrote:
>>> I really think that this proposal needs to focus on the short, simple
>>> use cases and *not* worry about too much generality. For example:
>>>
>>>     sum(x[3] except 0 for x in list_of_tuples)
>>>
>> Shouldn't that be:
>>
>>
>>     sum(x[3] except: 0 for x in list_of_tuples)
>>
>> (colon added)?
>
> Only if you feel that a colon is necessary for the syntax. I don't :-)

The colon is necessary if the new syntax should allow the
specification of the exception. If it's always equivalent to a bare
except that doesn't capture the exception object, then it'd be
unnecessary.

Personally, I don't want to create a special syntax that does
something that's strongly discouraged. I'm open to argument that the
expression-except should accept just a single except clause; I'm open
to argument that it shouldn't be able to capture (due to complications
of creating sub-scopes), though that's more a nod to
implementation/specification difficulty than any conceptual dislike of
the syntax (it's clean, it's consistent, it's sometimes useful); but I
don't want to narrow this down to always having to catch everything.

ChrisA