Chain asyncio coroutines inline in asyncio.gather

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I have a hypothetical asyncio.gather scenario:

await asyncio.gather(
    cor1,
    [cor2, cor3],
    cor4,
)

I'd like cor2 and cor3 to be executed in order here. Is there some shortcut way of doing other than defining an outside coroutine like this:

async def cor2_cor3():
    await cor2
    await cor3

await asyncio.gather(
    cor1,
    cor2_cor3,
    cor4,
)

Is there a cleaner shortcut for this?

python-asyncio python
1 Answers

Is there a cleaner shortcut for this?

asyncio doesn't provide one out of the box. If asyncio tasks had a method equivalent to JavaScript's Promise.then, you'd be able to use asyncio.create_task(cor2()).then(cor3()). But the asyncio equivalent, add_done_callback, is a more low-level construct which just sets up the callback without creating a new future, which makes it inconvenient for chaining.

To execute coroutines in order you will need to write a simple utility function, for example (untested):

async def chain(*aws):
    ret = None
    for aw in aws:
        ret = await aw
    return ret

Then you can invoke gather as:

await asyncio.gather(cor1(), chain(cor2(), cor3()), cor4())
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