The types.coroutine decorator for Python 3.6 (and I suspect for Python 3.6.1 as well) simply monkey patches the function it's passed and then returns it. This results in behavior that I found somewhat surprising.

def bar():
   yield 5

foo = types.coroutine(bar)

foo is bar

And, so now both foo and bar are now awaitable. I wasn't really expecting this, and while it's minor, it also doesn't really seem like the right thing to do.

Yes, that looks wrong to me.  IMO it should be returning a new function object, not updating the __code__ of the existing object.  I couldn't figure when that is actually triggered, though.  

There are also some other oddnesses, given the definition of 'coroutine' in the 'types' module docs.  type(x) returns 'coroutine' only when you actually *call* the async def function.  I think that's correct, but the docs need rewording.  However, if I call coroutine on the equivalent non-async-def generator, types(x()) returns generator, not coroutine.  So it doesn't seem to be doing what it says on the label, at least not in all cases.

Oops, I didn't meant to close this.

Yeah, we can fix this. However, I don't want to push the fix to 3.6, too much code uses this function now. So it's going to be 3.7 only.

Here's an update to types.coroutine that fixes the problem for me.