QUERY · ISSUE

uasyncio: Code throws exception under CPython

openby peterhinchopened 2020-06-19updated 2020-06-21

extmod

MicroPython allows a task to be created before issuing .run() but CPython throws an exception.

try:
    import uasyncio as asyncio
except ImportError:
    import asyncio

async def foo():
    await asyncio.sleep(3)

async def bar():
    await foo_task

foo_task = asyncio.create_task(foo())  # Naughty code here...
asyncio.run(bar())

Outcome under CPython 3.8.0:

adminpete@debian8:/mnt/qnap2/temp$ python3 -m rats_x
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/local/lib/python3.8/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/mnt/qnap2/temp/rats_x.py", line 12, in <module>
    foo_task = asyncio.create_task(foo())
  File "/usr/local/lib/python3.8/asyncio/tasks.py", line 381, in create_task
    loop = events.get_running_loop()
RuntimeError: no running event loop
sys:1: RuntimeWarning: coroutine 'foo' was never awaited

My view is that this doesn't matter, but I thought it worth reporting.

CANDIDATE · ISSUE

uasyncio gather() return_exceptions behaviour differs from CPython

closedby peterhinchopened 2021-09-16updated 2022-03-30

extmod

I think this is a regression. The following script produces an unexpected result in MicroPython:

try:
    import uasyncio as asyncio
except ImportError:
    import asyncio

async def will_stop(n):
    print('Runs to completion')
    for _ in range(6):
        await asyncio.sleep(1)
    return 2 * n

async def forever(n):
    print('forever() will be cancelled')
    while True:
        await asyncio.sleep(1)
        n += 1
    return n

async def do_cancel(task):
    await asyncio.sleep(3)
    print('About to cancel forever')
    task.cancel()

async def main():
    tasks = [asyncio.create_task(forever(70))]
    tasks.append(will_stop(21))
    asyncio.create_task(do_cancel(tasks[0]))
    res = None
    try:
        res = await asyncio.gather(*tasks, return_exceptions=True)
    except asyncio.CancelledError:
        print('Cancelled')
    print('Result: ', res)

asyncio.run(main())

CPython (expected behaviour):

adminpete@debian8:/mnt/qnap2/temp$ python3
Python 3.8.0 (default, Dec  6 2019, 16:20:13) 
[GCC 4.9.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import rats40
forever() will be cancelled
Runs to completion
About to cancel forever
Result:  [CancelledError(), 42]
>>>

MicroPython (behaves as if return_exceptions==False):

MicroPython v1.17 on 2021-09-02; linux version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> import rats40
forever() will be cancelled
Runs to completion
About to cancel forever
Cancelled
Result:  None
>>>

uasyncio: Code throws exception under CPython

uasyncio gather() return_exceptions behaviour differs from CPython

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