set, dict and other structures

[bearophileHUGS at lycos.com]

You are really gentle Raymond Hettinger, but surely I'm not asking
you/anyone to write some code just for me; I don't have "real
applications", I'm just learning/playing.
Your words are quite good answers to most of my questions.
The only left small topic is about the group/set-like
operations/methods added to dicts; maybe some other person can comment
that idea too. The semantic of such operations can be a little tricky,
but sometimes they can avoid the use of sets (and the set-ify of
dicts), sometimes they can carry the dict values with them (even if
they work just on the dict keys), etc.

A bear hug,
Bearophile