[Python-Dev] A more flexible task creation (original) (raw)

Michel Desmoulin desmoulinmichel at gmail.com
Fri Jun 15 04:08:21 EDT 2018

The strict API compatibility requirements of core Python stdlib, coupled with the very long feature release life-cycles of Python, make me think this sort of thing perhaps is better built in an utility library on top of asyncio, rather than inside asyncio itself?  18 months is a long long time to iterate on these features.  I can't wait for Python 3.8...

A lot of my late requests come from my attempt to group some of that in a lib: https://github.com/Tygs/ayo

Most of it works, although I got read of context() recently, but the lazy task part really fails.

Indeed, the API allows to do:

    async with ayo.scope() as run:
        task_list = run.all(foo(), foo(), foo())
        run.asap(bar())
        await task_list.gather()
        run.asap(baz())

scope() return a nursery like object, and this works perfectly, with the usual guaranty of Trio's nursery, but working in asyncio right now.

However, I tried to add to the mix:

    async with ayo.scope(max_concurrency=2) as run:
        task_list = run.all(foo(), foo(), foo())
        run.asap(bar())
        await task_list.gather()
        run.asap(baz())

And I can get it to work. task_list will right now contains a list of tasks and None, because some tasks are not scheduled immediately. That's why I wanted lazytasks. I tried to create my own lazy tasks, but it never really worked. I'm going to try to go down the road of wrapping the unscheduled coro in a future-like object as suggested by Yuri. But having that built-in seems logical, elegant, and just good design in general: init should not have side effects.

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