FIX: remove ipython import warning from top-level shap import

[connortann]

Fixes #3086

Removes the warning raised in _image.py if Ipython is not installed, and instead lazily raises an ImportError if the relevant function is called.

Also raises a more informative error in _text.py, where IPython's HTML and display functions may not be defined if not imported.

[codecov]

Codecov Report

Merging #3090 (c1622c7) into master (bf0adf8) will decrease coverage by 0.01%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##           master    #3090      +/-   ##
==========================================
- Coverage   55.35%   55.35%   -0.01%     
==========================================
  Files          90       90              
  Lines       12873    12881       +8     
==========================================
+ Hits         7126     7130       +4     
- Misses       5747     5751       +4     

Impacted Files	Coverage Δ
shap/__init__.py	68.33% <33.33%> (ø)
shap/plots/_text.py	54.45% <36.36%> (+0.04%)	⬆️
shap/plots/_image.py	73.04% <57.14%> (-1.07%)	⬇️

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[LukeHankey]

There is also a similar error message at shap/__init__.py:22 for matplotlib. Should this be changed from a ValueError to an ImportError?

[connortann]

I also propose changing the import warning in shap.__init__.py to a full ImportError. If the plotting functions are called and do not work, an explicit exception seems appropriate.

[LukeHankey]

I also propose changing the import warning in shap.__init__.py to a full ImportError. If the plotting functions are called and do not work, an explicit exception seems appropriate.

In that case, you won't need to import warnings in shap.__init__.py then