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[Python-Dev] PEP 526 ready for review: Syntax for Variable and Attribute Annotations


+0. We should try and be consistent even if this is a thing I don't
want. And trust me, I don't!

That said, as long as pro-mypy people are willing to make everyone else pay
a mypy reading tax for code let's try and reduce the cognitive burden.

* Duplicate type annotations should be a syntax error.
  Duplicate annotations aren't possible in functions so that wasn't an
issue in 484. 526 makes some things syntax errors and some things runtime
errors (for good reason -- function bodies aren't evaluated right away).
Double-annotating a variable is something we can figure out at compile time
and doing the double annotating is non-sensical so we should error on it
because we can.

*  Dissallowing annotations on global and nonlocal
  Agreed, allowing it would be confusing because it would either be a
re-definition or a hard to read annotation-at-a-distance.

* Where __annotations__ live
  It is strange to allow modules.__annotations__ and
MyClass.__annotations__ but not myfunc.__annotations__ (or more in line
with existing function implementations a myfunc.__code__.co_annotations).
If we know enough from the syntax parse to have func.__code__.co_varnames
be known then we should try to do that with annotations.  Let's raise a
SyntaxError for function body annotations that conflict with same-named
variables that are annotated in the function signature as well.

I did C++ for years before I did Python and wrote C++ in many languages
(including Python). So ideally I'm -1000 on all this stuff for cultural
reasons -- if you let a C++ person add types they will for false comfort.
But again, I'm +0 on this specific proposal because we have already gone
down the garden path.

-Jack


On Tue, Aug 30, 2016 at 9:00 PM, Steven D'Aprano <steve at pearwood.info>
wrote:

> On Tue, Aug 30, 2016 at 02:20:26PM -0700, Guido van Rossum wrote:
> > I'm happy to present PEP 526 for your collective review:
>
> Are you hoping to get this in before 3.6 beta? Because I'm not sure I
> can give this much attention before then, but I really want to.
>
>
> --
> Steve
> _______________________________________________
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>
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