fix: always run a coroutine and work with tornado

[maartenbreddels]

This is a port of what I use in vaex

This has been running for quite a while on CI, and seems pretty solid. If an event loop is present it will patch it with nested-asyncio and will also patch tornado, which should solve:

• RuntimeError: You are trying to run nbclient in an environment where an event loop is already running. Please pass nest_asyncio=True in NotebookClient.execute and such methods. nteract/papermill#490

Alternative to #67

See also erdewit/nest_asyncio#23 and tornadoweb/tornado#2753

This also checks to see if it is being run in an IPython context (I'm not sure the check makes sense, I just check if it is imported), and will give an error if not v7+, otherwise cells in a notebook may run out of order (a known? issue with older versions of IPython I believe), see also erdewit/nest_asyncio#9

[davidbrochart]

We might want to do that only once if we had a loop, not at each coroutine execution?

[maartenbreddels]

Well, the patch is not applied when tornado is not imported (this happens in vaex, where I first call this function, then start the server, and call this function again). Also the patch is only applied once (it checks if the Future is in the set).

[davidbrochart]

OK, but what about check_ipython() and nest_asyncio.apply()?

[maartenbreddels]

For check_ipython the same holds (it can be imported later on), and nest_asyncio has a check build in, in the end, simplicity, otherwise we need to check things that nest_asyncio already checks.

[davidbrochart]

Awesome work @maartenbreddels!

[maartenbreddels]

My problem with this PR is that I don't have a test, I have trouble reproducing the original issue. So lets put it to draft first.

[maartenbreddels]

Using the private API asyncio._get_running_loop() is the most portable way it seems to find out of we have a running ioloop.

[davidbrochart]

Thanks a lot for the tests and the awesome work!

[MSeal]

LGTM, let's give it a try. I am about to pop out an alpha 0.4 release for folks to try some of the recently merged changes this week anyway.

[MSeal]

0.4.0a0 is released fyi