[Python-Dev] Add a "transformdict" to collections

[Antoine Pitrou]

Le Tue, 10 Sep 2013 15:09:56 +0200,
Hrvoje Niksic <hrvoje.niksic at avl.com> a écrit :
> On 09/10/2013 02:24 PM, Paul Moore wrote:
> >>>> td['FOO'] = 42
> >>>> td['foo'] = 32
> >>>> list(td.keys())
> >
> > ['FOO'] or ['foo']? Both answers are justifiable.
> 
> Note that the same question can be reasonably asked for dict itself:
> 
>  >>> d = {}
>  >>> d[1.0] = 'foo'
>  >>> d[1] = 'bar'
>  >>> d
> {1.0: 'bar'}
> 
> So, dict.__setitem__ only replaces the value, leaving the original
> key in place. transformdict should probably do the same, returning
> 'FOO' in your example.

It's not that obvious. It's not common to rely on that aspect of dict
semantics, because you will usually lookup using the exact same type,
not a compatible one. I would expect very little code, if any, to rely
on this.

(also, I would intuitively expect the latest key to be held, not the
first one, since that's what happens for values.)

Regards

Antoine.