[Python-ideas] PEP 484 (Type Hints) -- first draft round
steve at pearwood.info
Thu Jan 22 15:55:33 CET 2015
On Thu, Jan 22, 2015 at 12:32:40PM +0000, Ed Kellett wrote:
> On Thu Jan 22 2015 at 12:17:37 Chris Angelico <rosuav at gmail.com> wrote:
> > The absence of a decorator that uses the annotations some other way
> > should make it clear that they're type hints, just as the absence of a
> > "global" statement should make it clear that assigned names are local
> > to a function.
> What about code that already exists?
What about them?
I have lots of code that already exists. (Some of it even works *wink*)
Since that code doesn't use annotations, this proposal will not make one
iota of difference to that code. *Literally* nothing will change.
Some of my code has annotations. But since I'm not using a PEP 484
type-checker on that code, it too will continue to work completely
The *only* code that will change is that which *I* decide to start using
annotations for type-checking. If I'm using Python 3.4 or older, I go to
PyPI and download the typing.py module. If I'm using 3.5, it will be
included in the standard library. So I add the annotations to my code:
as much, or as little, of the code as I choose. I could annotate as
little as one function or as much as the entire application.
Even then, I still have choices. I can choose whether to perform
type-checking or not:
- I can just run my code directly with the standard CPython interpreter
(the one you are probably using now), and no type-checks will take
place. CPython will not include a type-checker, not in 3.5 and perhaps
- I can run my code with Mypy, and it will perform static type-checks
before executing the code.
- I can run my code with a static linter or type-checker and not
run the code.
- Or just let my IDE or editor give me better completion hints and flag
errors as I type them.
> What about modules that want to
> support Python installations that already exist (hence don't have the
> `typing` module)?
typing.py will be available on PyPI.
> What about module authors who simply don't want to make
> their code ugly with a no-op decorator just to signify that they're not
> making it ugly with type annotations?
You don't need to flag functions with a decorator to signify that you
aren't using annotations. You just don't use annotations. Nobody (except
maybe your boss) will force you to use annotations. Python will continue
to work with them or without them.
The only people who end up a little worse off are those who already use
annotations for something else. But even they won't be *much* worse off,
just a little:
- Nobody will force them to use a type-checker or mypy, they can just
keep using their annotations and *not* use a type-checker.
- If they want to interoperate with a type-checker, they will have to
take steps to tell the type-checker to skip their annotations. This
might be a directive "# typing=OFF" or a "@notyping" decorator.
Either way, it won't be onerous.
- The worst case is if they want to use their existing annotations
AND the new type-hints at the same time, for the same functions.
In that case, they will have to find an alternative for their
annotations, perhaps moving them into a decorator.
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