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

[Bill Winslow]

Oh dear lord, it's like a nightmare where you're late to class without
clothing... except it actually happened... I knew something like this would
happen when I decided to actually do something.




On Fri, Aug 15, 2014 at 6:50 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> On 15 August 2014 21:01, Bill Winslow <bunslow at gmail.com> wrote:
> > Consider the following:
> >
> >
> >>>> from collections import abc as types
> >>>> isinstance(dict, types.Mapping)
> > False
> >>>> isinstance(types.Mapping, dict)
> > False
> >>>> isinstance(list, types.MutableSequence)
> > False
> >>>> isinstance(types.MutableSequence, list)
> > False
> >>>> isinstance(list, types.Sized)
> > False
>
> You're doing instance checks on subclasses - that's never going to
> work. Once you account for the type/instance distinction, you can see
> everything is correctly registered:
>
> >>> from collections import abc as cabc
> >>> issubclass(dict, cabc.Mapping)
> True
> >>> issubclass(list, cabc.Sequence)
> True
> >>> issubclass(list, cabc.Sized)
> True
> >>> isinstance(dict(), cabc.Mapping)
> True
> >>> isinstance(list(), cabc.Sequence)
> True
> >>> isinstance(list(), cabc.Sized)
> True
>
> (in Python 2, a couple of builtins claim ABCs they don't actually
> implement fully, but that's addressed in newer versions of Python 3)
>
> Cheers,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
>
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