[Python-Dev] PEP 492 vs. PEP 3152, new round

[Guido van Rossum]

On Wed, Apr 29, 2015 at 3:46 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
wrote:

> Yury Selivanov wrote:
>
>> I'm not sure
>> why Greg is pushing his Grammar idea so aggressively.
>>
>
> Because I believe that any extra complexity in the grammar
> needs a very strong justification. It's complexity in the
> core language, like a new keyword, so it puts a burden on
> everyone's brain.
>
> Saying "I don't think anyone would ever need to write this,
> therefore we should disallow it" is not enough, given that
> there is a substantial cost to disallowing it.
>
> If you don't think there's a cost, consider that we *both*
> seem to be having trouble predicting the consequences of
> your proposed syntax, and you're the one who invented it.
> That's not a good sign!
>

I have a slightly different view. A bunch of things *must* work, e.g.
f(await g(), await h()) or with await f(): (there's a longer list in the
PEP). Other things may be ambiguous to most readers, e.g. what does await
f() + g() mean, or can we say await await f(), and the solution is to
recommend adding parentheses that make things clear to the parser *and*
humans. Yury's proposal satisfies my requirements, and if we really find
some unpleasant edge case we can fix it during the 3.5 release (the PEP
will be provisional).

-- 
--Guido van Rossum (python.org/~guido)
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