[Python-Dev] PEP 492: async/await in Python; version 4

Guido van Rossum guido at python.org
Tue May 5 22:38:15 CEST 2015

Jumping in to correct one fact.

On Tue, May 5, 2015 at 12:44 PM, Brett Cannon <brett at python.org> wrote:

> On Tue, May 5, 2015 at 3:14 PM Paul Moore <p.f.moore at gmail.com> wrote:
>> Well, twisted always had defer_to_thread. Asyncio has run_in_executor,
>> but that seems to be callback-based rather than coroutine-based?
> Yep.

The run_in_executor call is not callback-based -- the confusion probably
stems from the name of the function argument ('callback'). It actually
returns a Future representing the result (or error) of an operation, where
the operation is represented by the function argument. So if you have e.g.
a function

    def factorial(n):
        return 1 if n <= 0 else n*factorial(n-1)

you can run it in an executor from your async(io) code like this:

    loop = asyncio.get_event_loop()
    result = yield from loop.run_in_executor(factorial, 100)

(In a PEP 492 coroutine substitute await for yield from.)

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