[Python-ideas] More general "for" loop handling

[Guido van Rossum]

On Thu, Apr 30, 2015 at 10:54 AM, Paul Moore <p.f.moore at gmail.com> wrote:

> On 30 April 2015 at 18:31, Guido van Rossum <guido at python.org> wrote:
> > PEP 492 is only meant to make code easier to read and write that's
> already
> > written to use coroutines (e.g. using the asyncio library, but not
> limited
> > to that).
>
> OK, that's fair. To an outsider like me it feels like a lot of new
> syntax to support a very specific use case. But that's because I don't
> really have a feel for what you mean when you note "but not limited to
> that". Are there any good examples or use cases for coroutines that
> are *not* asyncio-based? And assuming you are saying that PEP 482
> should help for those as well, could it include a non-asyncio example?
> My immediate reaction is that the keywords "async" and "await" will
> seem a little odd in a non-asyncio context.
>

The async/await pair of keywords for coroutines actually stems from C#,
where the compiler generates special coroutine suspension code when it sees
them, and the type checker verifies that they are used correctly -- await's
argument must be something of type async, and await must occur inside a
function declared as async. These semantics are very similar to coroutines
using yield-from in Python, and I had observed the similarity long before
this PEP was written.

Most examples of coroutines will be doing some kind of I/O multiplexing,
because that's what they're good for. But asyncio is not the only explicit
I/O multiplexing system in the Python world. Twisted had yield-based
coroutines long before anyone else (they called them InlineCallbacks
though) and is likely to support Python 3 and some level of
interoperability with asyncio.

Note: it's PEP 492, not 482.

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