[Python-ideas] Optional static typing -- the crossroads

[Guido van Rossum]

On Fri, Aug 15, 2014 at 9:48 AM, Petr Viktorin <encukou at gmail.com> wrote:

> On Fri, Aug 15, 2014 at 5:55 PM, Guido van Rossum <guido at python.org>
> wrote:
> ...
> >> Also... Does None magically mean NoneType in type definitions?
> >
> > Yes.
>
> This would mean either that `(None | None) is None`, or that (x |
> None) is not always "optional x".
> And if type objects grow any other common functionality, None will
> have to support that as well.
>

Perhaps None itself should not implement any of this, and the __ror__
method on ABCs should implement it. That way, None|Mapping and Mapping|None
would both work, yet None|None would still be the TypeError it is today.

-- 
--Guido van Rossum (python.org/~guido)
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