[Python-Dev] PEP 484 (Type Hints) -- the next draft is here

[Stefan Behnel]

Guido van Rossum schrieb am 18.04.2015 um 18:38:
> That's a good question. We *could* make it so that you can subclass
> Generator and instantiate the instances; or we could even make it do some
> structural type checking. (Please file a pull request or issue for this at
> github.com/ambv/typehinting .)

Done:

https://github.com/ambv/typehinting/issues/89


> But perhaps we should also change asyncio?
> What check are you talking about?

https://hg.python.org/cpython/file/439517000aa2/Lib/asyncio/coroutines.py#l169

The current (3.5alpha) check in iscoroutine() is an instance check against
_COROUTINE_TYPES, which contains types.GeneratorType and another wrapper
type. It excludes objects that implement the coroutine protocol without
being Python generators, e.g. Cython compiled generators, which mimic the
Python generator interface without having byte code in them (meaning, they
are not C-level compatible with Python generators). I'm sure the same
applies to other compilers like Numba or Nuitka. Supporting asyncio in
recent Python releases thus means monkey patching _COROUTINE_TYPES and
adding another type to it. Given that it's not a public interface, this
seems a bit fragile.

It also seems that this code only appeared somewhere in the 3.4.x release
series. Older versions were even worse and did a straight call to
inspect.isgenerator() in their iscoroutine() function, which means that the
whole function needed to be replaced and wrapped (and even that didn't fix
all places where inspect was used).

I guess I should open a (CPython) ticket for this topic, too...

Stefan