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[Python-Dev] Please reject or postpone PEP 526

Chris Angelico rosuav at gmail.com
Sun Sep 4 06:57:15 EDT 2016 
On Sun, Sep 4, 2016 at 8:52 PM, Mark Shannon <mark at hotpy.org> wrote:
> The key difference is in placement.
> PEP 484 style
> variable = value # annotation
>
> Which reads to me as if the annotation refers to the value.
> PEP 526
> variable: annotation = value
>
> Which reads very much as if the annotation refers to the variable.
> That is a change in terms of semantics and a change for the worse, in terms
> of expressibility.

So what you have is actually a change in *implication* (since the PEP
doesn't stipulate semantics); and the old way (the comment) implies
something contrary to the semantics of at least one of the type
checkers that uses it (MyPy). Are there any current type checkers that
actually do associate that with the value? That is, to have "variable
= func() # str" indicate the same type check as "def func() -> str"?
If not, this is a strong argument in favour of the PEP, since it would
synchronize the syntax with the current best-of-breed checkers.

ChrisA
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