BUG: __repr__ crashes in IPython if ipywidget isn't installed

[neutrinoceros]

ipython -c "import yt; ds=yt.load_sample('ChollaSimple'); ds.fields"

crashes with

ModuleNotFoundError: No module named 'ipywidgets'

Using the default python interpreter doesn't cause a crash

Note that I'm using the ChollaSimple sample dataset here only because it's small, but this bug isn't specific to the cholla frontend.

Originally posted by @neutrinoceros in #4054 (comment)

[neutrinoceros]

I can't find a way to fix this while keeping ipywidget an optional dependency. Given that it's a very light weighted, well maintained, pure Python package, I think the reasonable fix is simply to promote it as a hard dependency

[matthewturk]

I'm a little surprised we can't find a way around it. I don't think ipywidgets is an issue, but any new transitive dependencies might be worth verifying.

…

On Sat, Oct 8, 2022, 6:48 AM Clément Robert ***@***.***> wrote: I can't find a way to fix this while keeping ipywidget an optional dependency. Given that it's a very light weighted, well maintained, pure Python package, I think the reasonable fix is simply to promote it as a hard dependency — Reply to this email directly, view it on GitHub <#4154 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAVXO24YZP5WMU2N35ABHLWCFNRBANCNFSM6AAAAAARAHDT6M> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[neutrinoceros]

ATM it's not transitive, we directly import it.
We might be able to make it optional depending how we deal with #4054 though (ping @cphyc)