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From: Paul Rubin <no.email@nospam.invalid>
Newsgroups: comp.lang.python
Subject: Re: Suggestion: make sequence and map interfaces more similar
Date: Wed, 30 Mar 2016 19:45:58 -0700
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Steven D'Aprano <steve@pearwood.info> writes:
> I want to see an actual application where adding a new key to a
> mapping is expected to change the other keys.

directory["mary.roommate"] = "bob"
directory["mary.address"] = None   # unknown address
...
directory["bob.address"] = "132 Elm Street"

Since Bob and Mary are roommates, they have the same address, so the
application might want to update both addresses once it learns one of
them.