[Python-ideas] Control Flow - Never Executed Loop Body

[Michel Desmoulin]

Le 23/03/2016 16:53, Andrew Barnert a écrit :
> On Mar 23, 2016, at 03:08, Michel Desmoulin <desmoulinmichel at gmail.com> wrote:
> 
>>> But I think it is a coherent proposal, even if it's not one I like. :)
>>
>> And what do you think about adding except clauses to if ? with ? while ?
> 
> Well, they don't have the problem that for has (for is already implicitly handling a specific exception in a specific way; none of them are), so they're coherent even without a solution to that problem.
> 
> (With has the additional problem that it may not be immediately obvious on first glance whether the exit gets calls before or after the except clause, but if so, people can read the docs the first time they come across it and remember it after that.)
> 
> But I also think they're even less necessary. They'd all be pure syntactic sugar for nesting the statement and a try/except, so we'd be making the language more complicated to learn and remember, and encouraging more code that isn't backward compatible. That's not a huge cost, but the benefit isn't very big either. For _really_ short cases, I think we want except expressions (PEP 463); for longish code, there's nothing wrong with an explicit try; the range for which hiding an implicit try inside if and while would really improve things is small enough that I don't think the benefit outweighs the cost.
> 

Would love to see except expression win, but hasn't been rejected by the
BDFL ? Plus it's not really related to the current proposal.

> But maybe some good examples of realistic 3-liners that are significantly improved by the change would convince me (and, more importantly, convince a majority of the others who are skeptical), so I'll keep an open mind.
> 

The more I think about it, the more I think it's bad idea. We are mixing
semantics of loops and exceptions or conditions and exceptions.

I withdraw this part of the "general exceptions" proposal. I'm going
back to the simpler and less dangerous proposal:

for stuff in foo:
   bar(stuff)
or:
   default()