[Python-Dev] Remove typing from the stdlib

[Steve Dower]

On 03Nov2017 0915, 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
> 
> I'm strongly in favor on such move.

I'm torn.

If not having typing installed means you can't use "Any" or "Optional" 
in an annotation, that basically kills the whole thing. Some primitives 
need to be there.

If annotations become glorified strings (which IMHO they should) and 
typing gains a function to parse those into type hints (which IMHO it 
should), then I'm in favour of splitting typing out. (Personally, if 
making every type hint a literal 'string' meant that I could avoid 
importing typing then I'd do it.)

However, if typing is split out then its API (specifically, the contents 
of typing.__all__ and their semantic meaning (e.g. "Iterable" means 
something with an "__iter__" method)) needs to stay in PEPs.

Static analysers using type hints encode much more information about 
these types than can be inferred statically from typing.py, which means 
the definitions should not change faster than Python x.*y*. Ideally, 
they would not change at all once released.

For example, my static analyser has an existing object representing 
iterables, since we've been inferring iterables for years. When I parse 
a type annotation and see "typing.Iterable", I'm going to just 
substitute my own implementation - the definition in typing.py isn't 
going to be used (or be useful). And because it has to map across 
languages, it has to be a hard-coded mapping that can't rely on 
typing.py at all.

Since the contents of typing.py will likely be completely ignored by my 
analyser, which means that I can't treat "whatever version of typing is 
installed" as ground truth. It needs to move slower or be purely 
additive. Being in the standard library is a nice easy way to ensure 
this - moving it out is a risk.

That said, because I don't care about the contents of the file, all the 
heavy execution stuff can totally be moved out. If typing in the stdlib 
became very trivial definitions or just a set of names to support 
searching/editors/forward-refs, and typing out of the stdlib had the 
ability to convert annotations into an object model that provides rich 
runtime introspection, I'd also be fine. At least then the interface is 
highly stable, even if the implementation (for those who use it) changes.

Cheers,
Steve