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Using iscoroutinefunction() on an object returned by functools.partial() should return True if the function wrapped was a coroutine function.
(a recursive loop like the one in asyncio/events.py get_function_source() may be what needs to be done)

Take a look at asyncio.events._get_function_source() which supports wrapped functions and functools.partial.
Can you propose a patch?
If iscoroutinefunction() becomes "expensive", we might make checks optional, only run them in debug mode.

I recall discussing this before (maybe on the tulip list). I am firmly against. It is a slippery slope -- why inspect a partial but not a lambda? Plus there is no use case.

> Plus there is no use case.
Mathieu: can you maybe give some examples? How are you using functools.partial with coroutines?

Using functools.partial with coroutines would be mostly out of convenience, in order to avoid having factories in that return parametrized coroutine functions. I guess in such cases it might be better to create a two-lines wrapper around partial() to make it return a coroutine rather than change the stdlib for that.
In the attached file is an example of such use, where EventNotifier is a Protocol which receives external events and triggers event handlers based on that, and where the add_event_handler function checks if the handler is a coroutine function. In which case it uses asyncio.async to schedule the handler call; otherwise it uses loop.call_soon.
You can close this, I guess.

Yeah, your "add event handler" routine shouldn't be so picky to insist that iscoroutinefunction() returns True. It should just call the thing and verify that it has returned a coroutine object (asyncio.iscoroutine()).

There are use cases for this. I hit the problem and eventually wound up here, so I'd like to make a case to re-open.
My project has a callback registry of asyncio handler routines.
register_callback(condition1, handler1)
register_callback(condition2, handler2)
...
I want to register many callbacks, but use only one handler and an argument to differentiate it. I realize our callback systems should provide for a cookie, but it doesn't. 
register_callback(condition1, functools.partial(handler, 'detail1'))
register_callback(condition2, functools.partial(handler, 'detail2'))
The callback registry makes sure iscoroutinefunction(handler) because we don't want to defer error checking to the distant future. But iscoroutinefunction() returns False for the partial function. I was hopeful that this might work, but alas, no:
register_callback(condition1,
 asyncio.coroutine(functools.partial(handler, 'detail1')))

Use a lambda instead of partial. It's more pythonic.