[Python-Dev] PEP 492: No new syntax is required (original) (raw)

Paul Sokolovsky pmiscml at gmail.com
Tue Apr 28 21:24:22 CEST 2015

Hello,

On Mon, 27 Apr 2015 08:48:49 +0100 Mark Shannon <mark at hotpy.org> wrote:

On 27/04/15 00:13, Guido van Rossum wrote: > But new syntax is the whole point of the PEP. I want to be able to > syntactically tell where the suspension points are in coroutines. Doesn't "yield from" already do that? > Currently this means looking for yield [from]; PEP 492 just adds > looking for await and async [for|with]. Making await() a function > defeats the purpose because now aliasing can hide its presence, and > we're back in the land of gevent or stackless (where anything can > potentially suspend the current task). I don't want to live in that > land. I don't think I was clear enough. I said that "await" is a function, not that is should be disguised as one.

Yes, you said, but it is not. I guess other folks left figuring that out for yourself, and it's worthy exercise. Hint: await appears to translate to GET_AWAITABLE and YIELD_FROM opcodes. If your next reply is "I told you so", then you again miss that "await" is a special Python language construct (effectively, operator), while the fact that its implemented as GET_AWAITABLE and YIELD_FROM opcodes in CPython is only CPython's implementation detail, CPython being just one (random) Python language implementation.

Reading the code, "GetAwaitableIter" would be a better name for that element of the implementation. It is a straightforward non-blocking function.

Based on all this passage, my guess is that you miss difference between C and Python functions. On C level, there're only functions used to implement everything (C doesn't offer anything else). But on Python level, there're larger variety: functions, methods, special forms (a term with a bow to Scheme - it's a function which you can't implement in terms of other functions and which may have behavior they can't have). "await" is a special form. The fact that it's implemented by a C function (or not exactly, as pointed above) is just CPython's implementation detail. Arguing that "await" should be something based on what you saw in C code is putting it all backwards.

-- Best regards, Paul mailto:pmiscml at gmail.com

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