IndexError While using the "Chain" Method on a function with @asyn.cancellable

Now I have a real issue: If you use the normal await style from the chain example e.g: result = await compute(x, y) on a function with an @asyn.cancellable decorator, it will throw an: IndexError: tuple index out of range Error. (File “asyn.py”, line 327, in new_gen)

https://github.com/peterhinch/micropython-async/blob/8239a3d8b9f19430a13606c1492d5bf9a18300eb/chain.py#L15

https://github.com/peterhinch/micropython-async/blob/8239a3d8b9f19430a13606c1492d5bf9a18300eb/asyn.py#L327

[peterhinch]

You are using the module incorrectly. There is a required syntax for calling an awaitable function. In the no-args case it is

try:
    import uasyncio as asyncio
except ImportError:
    import asyncio
import asyn

@asyn.cancellable
async def compute():
    # No args are given to the compute function.
    print("compute function")
    await asyncio.sleep(1.0)
    return 1

async def print_sum(x, y):
    print("compute function")
    result = await asyn.Cancellable(compute)
    print(result)

loop = asyncio.get_event_loop()
loop.run_until_complete(print_sum(1, 2))
loop.close()

Or when passing args it is:

try:
    import uasyncio as asyncio
except ImportError:
    import asyncio
import asyn

@asyn.cancellable
async def compute(x, y):
    # No args are given to the compute function.
    print("compute function")
    await asyncio.sleep(1.0)
    return x + y

async def print_sum(x, y):
    print("compute function")
    result = await asyn.Cancellable(compute, x, y)
    print(result)

loop = asyncio.get_event_loop()
loop.run_until_complete(print_sum(1, 2))
loop.close()

[EDIT] This isn’t the first time this has caused confusion. I have updated PRIMITIVES.md to include a warning about this.

Incidentally my fast_io fork fixes this bug in uasyncio V2. Tasks may be cancelled in the normal way without the need for special syntax. Paul Sokolovsky’s version fixes this bug in a more efficient way but it requires his pycopy firmware; mine uses official firmware.

[peterhinch]

I found out about pycopy

This is your choice. I only support official MicroPython firmware for a few reasons, not least because binaries are available to those who are reluctant or unable to build from source.