Coroutine function detection procudes false negatives

[vxgmichel]

Here are the list of the combinators using asyncio.iscoroutinefunction to automatically detect whether the provided callback should be awaited or not:

• stream.accumulate
• stream.map
• stream.starmap
• stream.call
• stream.action
• stream.filter
• stream.until
• stream.dropwhile
• stream.takewhile

The problem with this detection is that it is hard to avoid false negatives.

However there are two counter-arguments to that:

• functools.partial has been fixed in python 3.8:

  assert asyncio.iscoroutinefunction(partial(asyncio.sleep, 3))

• aiostream provides an async_ helper to force the argument to be treated as a coroutine function:

  ys = stream.map(xs, async_(lambda x: asyncio.sleep(x / 1000))

I can see a few solutions here:

• Duplicate all those functions and give them explicit names (e.g filter_sync, filter_async). Problem: I don't like the idea of duplicating all those operators
• Implement some other kind of detection, for instance check if the result is awaitable. Problem: it becomes impossible to use awaitables as elements of a stream.
• Perform a detection to issue a warning if a sync function returns an awaitable, mentioning the use of async_ to fix the warning. Problem: does not fully address the initial issue.

Are there other alternative?