[Python-Dev] Is static typing still optional? (original) (raw)

Chris Barker chris.barker at noaa.gov
Thu Dec 21 19:07:46 EST 2017

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

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Christopher Barker, Ph.D. Oceanographer

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