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

[Michael Selik]

> 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.