[Python-Dev] Compact ordered set

Antoine Pitrou solipsis at pitrou.net
Thu Feb 28 06:56:55 EST 2019

On Thu, 28 Feb 2019 22:43:04 +1100
Steven D'Aprano <steve at pearwood.info> wrote:
> On Wed, Feb 27, 2019 at 02:15:53PM -0800, Barry Warsaw wrote:
> > I’m just relaying a data point.  Some Python folks I’ve worked with do 
> > make the connection between dicts and sets, and have questions about 
> > the ordering guarantees of then (and how they relate).  
> Sets and dicts are not related by inheritence (except that they're both 
> subclasses of ``object``, but so is everything else). They don't share 
> an implementation. They don't provide the same API. They don't do the 
> same thing, except in the most general sense that they are both 
> collections.
> What connection are these folks making?

Some of them may be coming from C++, where the respective
characteristics of set and map (or unordered_set and
unordered_multimap) are closely related.  I'm sure other languages
show similar analogies.

On a more abstract level, set and dict are both content-addressed
collections parametered on hash and equality functions.  For
algorithmically-minded people it makes sense to see a close connection
between them.



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