[Python-Dev] PEP 492 vs. PEP 3152, new round (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Wed Apr 29 03:51:51 CEST 2015

Looking at the grammar -- the only downside of the current approach is that you can't do 'await await fut'. I still think that it reads better with parens. If we put 'await' to 'factor' terminal we would allow

 await -fut  # await (-fut)

I think I something like

 power: atom_expr ['**' factor]
 atom_expr: [AWAIT] atom_expr | atom_trailer
 atom_trailer: atom trailer*

will fix 'await await' situation, but does it really need to be fixed?

Yury

On 2015-04-27 9:44 AM, Yury Selivanov wrote:

Hi Greg,

I don't want this: "await a() * b()" to be parsed, it's not meaningful. Likely you'll see "await await a()" only once in your life, so I'm fine to use parens for it (moreover, I think it reads better with parens) Yury

On 2015-04-27 8:52 AM, Greg Ewing wrote: Yury Selivanov wrote: I've done some experiments with grammar, and it looks like we indeed can parse await quite differently from yield. Three different options:

You don't seem to have tried what I suggested, which is to make 'await' a unary operator with the same precedence as '-', i.e. replace factor: ('+'|'-'|'~') factor | power with factor: ('+'|'-'|'~'|'await') factor | power That would allow await a() res = await a() + await b() res = await await a() if await a(): pass return await a() print(await a()) func(arg=await a()) await a() * b()

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