Python typings and futures

Question

I'm very glad to use typing module in Python 3. Also, I'm very glad to use asyncio instead of twisted, tornado and alternatives.

My question is how to define result of a coroutine properly?

Should we tell it's just a coroutine? Example 1:

async def request() -> asyncio.Future:
    pass

Or should we define type of result of coroutine as type of returning value? Example 2:

async def request() -> int:
    pass

If yes, then how to be with plain functions, which return futures? Example 3:

def request() -> asyncio.Future:
    f = asyncio.Future()
    # Do something with the future
    return f

Is it a right way? How then we can tell what is expected to be a result of the future?

Use the generic versions, e.g. https://docs.python.org/3/library/typing.html#typing.Awaitable — jonrsharpe, Jul 15 '17 at 08:33

score 3 · Accepted Answer · answered Jul 15 '17 at 16:47

3

As @jonrsharpe said, typing.Awaitable perfectly suits the task.

answered Jul 15 '17 at 16:47

oblalex

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score 3 · Answer 2 · answered Jul 15 '17 at 19:28

3

In general, you should regular return value (such as int, float, bool, None and etc), but if you use it as a callable it should look like this:

async def bar(x: int) -> str:
    return str(x)

cbar: Callable[[int], Awaitable[str]] = bar

For more information: here.

You can look at this issue also for mypy support.

answered Jul 15 '17 at 19:28

Yuval Pruss

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As for a type of the function, yes, that's true. But question was only about function's return type. Anyway, thank you – oblalex Jul 17 '17 at 17:39

Python typings and futures

2 Answers2