[Python-Dev] Remove typing from the stdlib

[Paul Moore]

On 3 November 2017 at 17:47, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Fri, 3 Nov 2017 12:46:33 -0400
> "Eric V. Smith" <eric at trueblade.com> wrote:
>> On 11/3/2017 12:15 PM, Victor Stinner wrote:
>> > Hi,
>> >
>> > 2017-11-03 15:36 GMT+01:00 Guido van Rossum <guido at python.org>:
>> >> Maybe we should remove typing from the stdlib?
>> >> https://github.com/python/typing/issues/495
>>
>> > The typing module is not used yet in the stdlib, so there is no
>> > technically reason to keep typing part of the stdlib. IMHO it's
>> > perfectly fine to keep typing and annotations out of the stdlib, since
>> > the venv & pip tooling is now rock solid ;-)
>>
>> I'm planning on using it for PEP 557:
>> https://www.python.org/dev/peps/pep-0557/#class-variables
>>
>> The way the code currently checks for this should still work if typing
>> is not in the stdlib, although of course it's assuming that the name
>> "typing" really is the "official" typing library.
>
> I don't think other modules should start relying on the typing module at
> runtime.
> The dataclasses module can define its own "ClassVar" thing and then I
> suspect it's easy to map it to typing._ClassVar.  It seems we should be
> careful not to blur the distinction between declarations that have an
> effect on actual code, and typing declarations which only affect
> type-checking tools.

I'm looking forward to the dataclasses module, and I'm perfectly OK
with the way that it uses type annotations to declare attributes. I
also don't have a problem with it relying on the typing module - but
*only* if the typing module is in the stdlib. I don't think it's good
if a standard feature needs an external library for some of its
functionality.

So I guess the point is, if we're considering moving typing out of the
stdlib, then what's the impact on PEP 557?

Personally, I don't use type annotations myself yet, but I've used
code that does and I'm considering looking into them - for a variety
of reasons, documentation, IDE support, and the ability to type check
my code via mypy. If typing moves out of the stdlib, I'd be much less
inclined to do so - adding a runtime dependency is a non-trivial cost
in terms of admin for deployment, handling within my (peculiar, if you
want to debate workflow) development workflow, etc. Working out how to
add type annotations *without* them being a runtime dependency (just
at test-time) is too much work. So I am concerned that if we move
typing out of the stdlib, it'll reduce adoption rates.

Paul