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[Python-Dev] Please reject or postpone PEP 526

Ivan Levkivskyi levkivskyi at gmail.com
Sun Sep 4 13:59:35 EDT 2016 
On 4 September 2016 at 19:29, Nick Coghlan <ncoghlan at gmail.com> wrote:

> So in this case, attempting to entirely defer specification of the
> semantics creates a significant risk of type checkers written on the
> assumption of C++ or Java style type declarations actively inhibiting
> the dynamism of Python code, suggesting that the PEP would be well
> advised to declare not only that the PEP 484 semantics are unchanged,
> but also that a typechecker that flags the example above as unsafe is
> wrong to do so.
>

I don't think that a dedicated syntax will increase the
risk more than the existing type comment syntax. Moreover,
mainstream type checkers (mypy, pytype, etc) are far
from C++ or Java, and as far as I know they are not going
to change semantics.

As I understand, the main point of Mark is that such syntax suggests
visually a variable annotation, more than a value annotation.
However, I think that the current behavior of type checkers will
have more influence on perception of people rather than a visual
appearance of annotation.

Anyway, I think it is worth adding an explicit statement to the PEP
that both interpretations are possible (maybe even add that value
semantics is inherent to Python). But I don't think that we should
*prohibit* something in the PEP.

--
Ivan
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