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

[Nick Coghlan]

On 2 August 2016 at 17:54, Paul Moore <p.f.moore at gmail.com> wrote:
> So in my view, allowing annotations on unpacking syntax is going to
> cause a *lot* of confusion, and I'd strongly argue for only allowing
> type annotations on single variables:
>
>     VAR [: TYPE] [= INITIAL_VALUE]
>
> For multiple variables, just use multiple lines:
>
>     a: int
>     b: str = x
>
> or
>
>     a: int
>     b: str
>     a, b = x
>
> depending on your intention.
>
> From what Guido says, the main use case is class variables, where
> complicated initialisations are extremely rare, so this shouldn't be a
> problem in practice.

+1 from me for this view: only allow syntactic annotation of single
names without parentheses. That one rule eliminates all the cases
where unpacking assignment and parameter assignment do starkly
different things.

*However*, even with that restriction, unambiguously annotated
unpacking could still be supported via:

    (a, b) : Tuple[int, str] = x
    (a, b, *c) : Tuple[int, int, Tuple[int]] = y

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia