RFC: improve readability of IPython-specific code blocks

[neutrinoceros]

Description

This has come up in #16354 (comment) :
basically neither @pllim or I knew how these blocks worked off-hand and it caused some confusion, so I'm trying to rewrite the logic in a (hopefully) clearer fashion.

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[pllim]

I think you can import _WITHIN_IPYTHON from logger.py instead of redefining it here?

[neutrinoceros]

done !

[pllim]

Thanks!