[Python-ideas] Trial balloon: adding variable type declarations in support of PEP 484

[Daniel Moisset]

There's something I found a bit confusing in the runtime semantic of
defaults in your strawman proposal:

On Tue, Aug 2, 2016 at 11:09 PM, Guido van Rossum <guido at python.org> wrote:

> Agreed, we need to invent a workable proposal for this. Here's a strawman:
>
> - The default is an instance variable (backed by a class variable as
> default if there's an initial value)
> - To define a class variable, prefix the type with 'class`
>
> Example:
>
> class C:
>     a: int  # instance var
>     b: List[int] = None  # instance var
>     c: class List[int] = []  # class var
>
>
>From that description I understand that after C is defined, C.__dict__ will
contain the {'c': []} mapping... where us the {'b': None} mapping stored?
what's the runtime semantics that get it to every created instance?

Or you are proposing that in runtime these are equivalent to "b, c = None,
[]" ? If that's the case, I find it misleading to call them "instance
variables" vs "class variables", given that those concepts are supposed to
have different runtime semantics, not just for the typechecker.


-- 
Daniel F. Moisset - UK Country Manager
www.machinalis.com
Skype: @dmoisset
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