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[Python-ideas] Dictionary views are not entirely 'set like'

Joshua Morton joshua.morton13 at gmail.com
Thu Apr 14 02:59:44 EDT 2016 
These were exactly my thoughts. I wanted to bump this, since it was drowned
out by more important things like Paths and invertible booleans and almost
no discussion was had on the main issue, that of dict views not acting like
sets. Since things have died down, is that behavior that should be
remedied, and if so should it be backwards compatible (make set more
permissive), treat it as a bugfix (make the views raise errors)? And should
it include union/other methods to keep performance on the usecase that now
throws a bug?

-Josh

On Thu, Apr 7, 2016 at 1:53 PM Michael Selik <mike at selik.org> wrote:

>
> > On Apr 6, 2016, at 10:38 AM, Joshua Morton <joshua.morton13 at gmail.com>
> wrote:
> >     set() | []  # 2
> >     {}.keys() | []  # 3
>
> Looks like this should be standardized. Either both raise TypeError, or
> both return a set. My preference would be TypeError, but that might be
> worse for backwards-compatibility.
>
> >     {}.keys().union(set())  # 6
>
> Seems to me that the pipe operator is staying on MappingView, so it's
> reasonable to add a corresponding ``.union`` to mimic sets. And
> intersection, etc.
>
> >     {}.values() == {}.values()  # 9
> >     d = {}; d.values() == d.values()  # 10
>
> It's weird, but float('nan') != float('nan'). I'm not particularly
> bothered by this.
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