Tornado not starting on Windows 10 / Python 3.8 breaks display()

[eamoore]

Charts are served to the Viewer via a background service implemented on Tornado.

On Windows 10, Python 3.8, Tornado won't start. This may apply to more Altair renderers than 'altair_viewer' and 'mimetype'. I am working outside a notebook environment (Jupyter, Collab, etc). Without Tornado, display() and show() don't work. Practically speaking, it looks like the best work around for a non notebook IDE or user around is to render charts to html (Chart.save()).

The stack trace points to asyncio,
asyncio\events.py", line 501, in add_reader raise NotImplementedError

This stackoverflow thread points a platform constraint:
https://stackoverflow.com/questions/54608421/how-to-fix-notimplementederror-when-trying-to-run-hydrogen-in-atom

If I am understanding the issue and workaround correctly, it might be worth mentioning in the doc, at https://altair-viz.github.io/user_guide/display_frontends.html#altair-viewer

[eamoore]

Following up, I implemented a recommended workaround (edit Lib/asyncio/init.py) and that solved the issue.

see https://stackoverflow.com/questions/58422817/jupyter-notebook-with-python-3-8-notimplementederror/58430041#58430041

I still think a heads up for Windows users would be good.