If IPython is merely installed, don't assume that it's actually used

[pfalcon]

In my virtual environment, there happens to be installed IPython package. It wasn't installed by myself, it's merely a transitive dependency of some another package. It's neither intended to be used, nor is actually used by my project. However, mere presense of the IPython package, due to the over-simplistic decision code in this module (io._renderers) leads to drastic behavior change in Plotly.py: calling Figure.repr_html() causes lots of JS garbage to be printed on terminal (by common sense, this should be a side-effects free function, only returning a value). On a higher level, this breaks natural Plotly.py integration in frameworks like Shiny.py (because again, instead of HTML representation being returned for a framework to process, parts of that representation are dumped on terminal).

The real underlying issue is that Plotly.py should not force-import any "optional" packages behind users' back. However, this is a deeper issue requiring consideration and will be reported separately. This patch is a quick solution for the problem describe above.

From interactive session:

>>> import IPython
>>> IPython.get_ipython().__class__.__name__
'NoneType'

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Code PR

• [x] I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the codegen files and not generated files.
• [ ] I have added tests (if submitting a new feature or correcting a bug) or modified existing tests.
• [ ] For a new feature, I have added documentation examples in an existing or new tutorial notebook (please see the doc checklist as well).
• [ ] I have added a CHANGELOG entry if fixing/changing/adding anything substantial.
• [ ] For a new feature or a change in behaviour, I have updated the relevant docstrings in the code to describe the feature or behaviour (please see the doc checklist as well).

[pfalcon]

Example of how this affects downstream projects: https://github.com/posit-dev/py-shinywidgets/issues/201 . I'm an experienced Python user, and it took me half a day to debug this issue. I imagine how frustrating it may be for novice users who just wanted to try one of those well-popularized modern Python data visualization packages.

[emilykl]

Hi @pfalcon , I've just merged a fix in https://github.com/plotly/plotly.py/pull/5258 which takes a slightly different approach to this same issue. Thank you for the contribution and please let me know if that fix addresses the issue on your end!