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From: Marco Sulla <mail.python.org@marco.sulla.e4ward.com>
Newsgroups: comp.lang.python
Subject: Re: Suggestion: make sequence and map interfaces more similar
Date: Thu, 31 Mar 2016 14:49:51 +0200
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Xref: csiph.com comp.lang.python:106151

I want also to add that we are focusing on sequences, but my proposal
is also to make map interface more similar, introducing a vdict type
that iterates over values, and this will be for me really more
practical. PEP 234 (  http://legacy.python.org/dev/peps/pep-0234/ )
never convinced me. Van Rossum said:

> The symmetry between "if x in y" and "for x in y"
> suggests that it should iterate over keys.  This symmetry has been
> observed by many independently and has even been used to "explain"
> one using the other.  This is because for sequences, "if x in y"
> iterates over y comparing the iterated values to x.

This argument will never convinced me. It's a lot more practical (as
Van Rossum admitted further) to iterate over values by default on
maps. Furthermore I see much more symmetry between keys of maps and
indexes of sequences, so it's much more natural to make map iteration
over values by default, as for sequences. This is why I proposed a
vdict.


On 31 March 2016 at 14:30, Mark Lawrence via Python-list
<python-list@python.org> wrote:
> Note that dict also supports
> __getitem__() and __len__(), but is considered a mapping rather than a
> sequence because the lookups use arbitrary immutable keys rather than
> integers.

Thank you for confirming for what I already wrote and quoted, but I suppose you
missed some of my previous messages, my dear friend.