On Tue, Apr 13, 2021 at 12:32 PM Larry Hastings <[email protected]
<mailto:[email protected]>> 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.