On Tue, Apr 13, 2021 at 12:32 PM Larry Hastings <la...@hastings.org> wrote:
>
> On 4/12/21 7:24 PM, Guido van Rossum wrote:
>
> I've been thinking about this a bit, and I think that the way forward is
> for Python to ignore the text of annotations ("relaxed annotation syntax"),
> not to try and make it available as an expression.
>
> To be honest, the most pressing issue with annotations is the clumsy way
> that type variables have to be introduced. The current convention, `T =
> TypeVar('T')`, is both verbose (why do I have to repeat the name?) and
> widely misunderstood (many help request for mypy and pyright follow from
> users making a mistaken association between two type variables that are
> unrelated but share the same TypeVar definition). And relaxed annotation
> syntax alone doesn't solve this.
>
> Nevertheless I think that it's time to accept that annotations are for
> types -- the intention of PEP 3107 was to experiment with different syntax
> and semantics for types, and that experiment has resulted in the successful
> adoption of a specific syntax for types that is wildly successful.
>
>
> I don't follow your reasoning. I'm glad that type hints have found
> success, but I don't see why that implies "and therefore we should restrict
> the use of annotations solely for type hints". Annotations are a useful,
> general-purpose feature of Python, with legitimate uses besides type
> hints. Why would it make Python better to restrict their use now?
>
Because typing is, to many folks, a Really Important Concept, and it's
confusing to use the same syntax ("x: blah blah") for different purposes,
in a way that makes it hard to tell whether a particular "blah blah" is
meant as a type or as something else -- because you have to know what's
introspecting the annotations before you can tell. And that introspection
could be signalled by a magical decorator, but it could also be implicit:
maybe you have a driver that calls a function based on a CLI entry point
name, and introspects that function even if it's not decorated.
OTOH, not requiring that annotations are syntactically valid expressions
might liberate such a CLI library too: you could write things like
def foo(prec: --precision int):
...
--
--Guido van Rossum (python.org/~guido)
*Pronouns: he/him **(why is my pronoun here?)*
<http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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