[Python-Dev] PEP 492 quibble and request

[Guido van Rossum]

On Wed, Apr 29, 2015 at 7:07 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> [...]
> Yeah, I'm coming around to the idea. For the async pseudo-keyword, I
> can see that the proposal only allows its use in cases that were
> previously entirely illegal, but I'm not yet clear on how the PEP
> proposes to avoid changing the meaning of the following code:
>
>     x = await(this_is_a_function_call)
>
> Unless I'm misreading the proposed grammar in the PEP (which is
> entirely possible), I believe PEP 492 would reinterpret that as:
>
>     x = await this_is_not_a_function_call_any_more
>

Ah, but here's the other clever bit: it's only interpreted this way
*inside* a function declared with 'async def'. Outside such functions,
'await' is not a keyword, so that grammar rule doesn't trigger. (Kind of
similar to the way that the print_function __future__ disables the
keyword-ness of 'print', except here it's toggled on or off depending on
whether the nearest surrounding scope is 'async def' or not. The PEP could
probably be clearer about this; it's all hidden in the Transition Plan
section.)

-- 
--Guido van Rossum (python.org/~guido)
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-dev/attachments/20150429/fe6d90ff/attachment.html>