[Python-Dev] Is static typing still optional?

[Chris Barker]

On Thu, Dec 21, 2017 at 3:36 PM, Gregory P. Smith <greg at krypto.org> wrote:


>  But we already have ... which does - so I'd suggest that for people who
> are averse to importing anything from typing and using the also quite
> readable Any.  (ie: document this as the expected practice with both having
> the same meaning)
>

I don't think they do, actually - I haven't been following the typing
discussions, but someone in this thread said that ... means "use the type
of teh default" or something like that.


> While I consider the annotation to be a good feature of data classes, it
> seems worth documenting that people not running a type analyzer should
> avoid declaring a type.
>

+1 !


> A worse thing than no-type being specified is a wrong type being
> specified. That appearing in a library will break people who need their
> code to pass the analyzer and pytype, mypy, et. al. could be forced to
> implement a typeshed.pypi of sorts containing blacklists of known bad
> annotations in public libraries and/or actually correct type specification
> overrides for them.
>

and the wrong type could be very common -- folks using "int", when float
would do just fine, or "list" when any iterable would do, the list goes on
and on. Typing is actually pretty complex in Python -- it's hard to get
right, and if you aren't actually running a type checker, you'd never know.

One challenge here is that annotations, per se, aren't only for typing. Bu
tit would be nice if a type checker could see whatever "non-type" is
recommended for dataclasses as "type not specified". Does an ellipses spell
that? or None? or anything that doesn't have to be imported from typing :-)

As for problems with order, if we were to accept
>
> @dataclass
> class Spam:
>     beans = True
>     ham: bool
>
> style instead, would it be objectionable to require keyword arguments only
> for dataclass __init__ methods?  That'd get rid of the need to care about
> order.
>

wouldn't  that make the "ham: bool" legal -- i.e. no default?

-CHB

-- 

Christopher Barker, Ph.D.
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