Cython used with async - Decorators can only be followed by functions or classes

[JendaPlhak]

I'm trying to compile Python 3 code using Cython (version 0.25a0). The code heavily depends on asyncio and works normally when run with latest Python. Compilation however gives me following error:

Error compiling Cython file:
------------------------------------------------------------
...

    @helpers.json_handler(logger = logger)
    async def get_index(req, req_body):
   ^
------------------------------------------------------------

skystore/mem_node.py:40:4: Decorators can only be followed by functions or classes

Does it mean, that async and await keywords are not supported? I thought otherwise because according to changelog it was implemented last year.

[robertwb]

I think this combination simply hasn't been implemented yet. It'd require a bit of plumbing, but hopefully it wouldn't be that hard.

[JendaPlhak]

I would be happy to help my self, but I never really touched Cython internals so I don't know whether I can be of any use :-/

[scoder]

Works for me. I guess async def wasn't actually implemented at the time.

[buckle2000]

This is not fully fixed! The following code won't compile.

# a.py
def pass_through(func):
    return func


async def another():
    @pass_through
    async def test_pass_through():
        pass

> cython -3 a.py

Error compiling Cython file:
------------------------------------------------------------
...
    return func


async def another():
    @pass_through
    async def test_pass_through():
   ^
------------------------------------------------------------

a.py:8:4: Decorators can only be followed by functions or classes

[scoder]

Ah, yeah, thanks for noticing. Turns out, decorators work for the first async def spotted, and that enables async as keyword. Afterwards, async is a keyword and is then no longer recognised in the parser code paths that accept decorators. :)

[scoder]

Actually, I think Cython 3.0 is a good time to generally make async a keyword for good.
Although – why break stuff that works…