change of behaviour in do_one_iteration(), and qt5 loop integration issues?

I was wondering: did something significant change in do_one_iteration() between 5.3.2 and 6.4.1?

I used to use this to process messages from ipywidgets during a loop, but this seems no longer possible:

https://stackoverflow.com/questions/70436504/problem-with-event-loops-gui-qt5-and-ipywidgets-in-a-jupyter-notebook

There was a slightly more complicated solution I found using asyncio but this also breaks if I need to use a qt5 gui loop.

I guess my questions are:

Is there a workflow that is still possible to how I previously was using do_one_iteration()?
Is there a solution to the got Future <Future pending> attached to a different loop problem when using a qt5 gui event loop?

Thanks!
Gary

@ccordoba12

@ccordoba12 might this be related to #531?

Minor update from my side: I recently restarted with a new environment.

The problem with the qt5 gui loop is still there (although warning about <Future pending> attached to a different loop is gone?)

I've also made a video if you want to see it live:

https://tudelft.zoom.us/rec/play/CgFo2_JIS8qdNQm8mJRwheOygc_CsCRmv4mNq4TIcvAnzPqLTzkNE0u6w0BlUrI2ckkvrQRXUlu0d3A8.TKUOmocoDlhmEG5n?continueMode=true&_x_zm_rtaid=chuscAkeT1OVGF1NZcosQQ.1641226261305.d72721c18f45943ad7e889aae4e8f2f5&_x_zm_rhtaid=584

(and posted on the ipywidgets discourse forum, but edited post too many times too quickly and it got marked as spam...i guess a staff member will unblock it)

I've also done some more reading into the low level implementation of the ipywidgets sync via the kernel COMMS interface. My guess is that coroutines running in the asyncio GUI event loop are somehow triggering the kernel to refresh and process received COMMS messages, but ones running in the qt5 GUI loop are not...?

I think the problem is that do_one_iteration is now a coroutine, so you can't expect to call it and get a response immediately. However, you can make it run synchronously again with asyncio.

A similar problem (I think) for the Tk was solved here: #830.

@ccordoba12

Thanks @ccordoba12 for pointing me in the right direction!

So if I understand correctly: if I install the latest version of ipykernel from github, then the following code should work as a replacement for my previous direct call of do_one_iteration()?

    task = loop.create_task(do_one_iteration())
    loop.run_until_complete(task)

Thanks!
Gary

I guess that I don't fully understand how to solve this issue.I just cloned and installed ipykernel from github:

Selected Jupyter core packages...
IPython          : 7.29.0
ipykernel        : 6.6.1
ipywidgets       : 7.6.5
jupyter_client   : 7.0.6
jupyter_core     : 4.9.1
jupyter_server   : not installed
jupyterlab       : not installed
nbclient         : 0.5.3
nbconvert        : 6.1.0
nbformat         : 5.1.3
notebook         : 6.4.6
qtconsole        : 5.1.1
traitlets        : 5.1.1

And I then tried the following, but apparently this is not the way:

import ipywidgets as widgets
from time import sleep
import IPython
import asyncio

do_one_iteration = IPython.get_ipython().kernel.do_one_iteration
loop = asyncio.get_running_loop()

w = widgets.ToggleButton()
display(w)

i=0
while True:
    # This one gives: "asyncio.run() cannot be called from a running event loop"
    # asyncio.run(do_one_iteration())
    
    # This one gives "QueueEmpty:"
    # await do_one_iteration()
    
    # the original one that worked, but now gives coroutine 
    # 'Kernel.do_one_iteration' was never awaited
    # and then updates are not propagated 
    # do_one_iteration()
    
    # This does not appear to be the solution results in 
    # RuntimeError: This event loop is already running
    task = loop.create_task(do_one_iteration())
    loop.run_until_complete(task)
  
    print(i, w.value, end="\r")
    w.decription = str(i)
    sleep(0.5)
    i+=1

as this gives an error:

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
/var/folders/5t/sp26pw315mnbcfyyt9l9bvpwqb6r8t/T/ipykernel_85521/4094668809.py in <module>
     26     # RuntimeError: This event loop is already running
     27     task = loop.create_task(do_one_iteration())
---> 28     loop.run_until_complete(task)
     29 
     30     print(i, w.value, end="\r")

~/anaconda3/envs/dec2021/lib/python3.9/asyncio/base_events.py in run_until_complete(self, future)
    616         """
    617         self._check_closed()
--> 618         self._check_running()
    619 
    620         new_task = not futures.isfuture(future)

~/anaconda3/envs/dec2021/lib/python3.9/asyncio/base_events.py in _check_running(self)
    576     def _check_running(self):
    577         if self.is_running():
--> 578             raise RuntimeError('This event loop is already running')
    579         if events._get_running_loop() is not None:
    580             raise RuntimeError(

RuntimeError: This event loop is already running

Any advice appreciated!

Thanks,
Gary

@impact27

Probably you need to use nest_asyncio first (sorry, I don't understand asyncio loops very well).

@impact27, do yo know how to run do_one_iteration directly?

Asyncio loops are not rentrant. But you can just use nest_asyncio for that. Just add to your script:

import nest_asyncio
nest_asyncio.apply()

Or in IPython:

In [2]: do_one_iteration = get_ipython().kernel.do_one_iteration

In [3]: await do_one_iteration()

Or in IPython:

In [2]: do_one_iteration = get_ipython().kernel.do_one_iteration

In [3]: await do_one_iteration()

This one doesn't work for me:

(was also one of my earlier attempts) I get an error "Queue Empty"

Asyncio loops are not rentrant. But you can just use nest_asyncio for that. Just add to your script:
import nest_asyncio
nest_asyncio.apply()

Amazing! Perfect! I don't understand it but it works :) Thanks!

Or in IPython:
In [2]: do_one_iteration = get_ipython().kernel.do_one_iteration

In [3]: await do_one_iteration()
This one doesn't work for me:

(was also one of my earlier attempts) I get an error "Queue Empty"

This is strange. You can even see in the traceback you attach where the error should be caught.

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change of behaviour in do_one_iteration(), and qt5 loop integration issues? #825

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change of behaviour in do_one_iteration(), and qt5 loop integration issues? #825

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blink1073 commented on Dec 24, 2021

gsteele13 commented on Jan 3, 2022

ccordoba12 commented on Jan 4, 2022

gsteele13 commented on Jan 5, 2022

gsteele13 commented on Jan 5, 2022

ccordoba12 commented on Jan 5, 2022

impact27 commented on Jan 5, 2022

impact27 commented on Jan 5, 2022

gsteele13 commented on Jan 5, 2022

gsteele13 commented on Jan 5, 2022

impact27 commented on Jan 5, 2022

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