[Python-Dev] Reserve ':=' for type-inferred variable initialization (was PEP 572)

[Andrea Griffini]

>> We're focused on Python 3.8 and 3.9, not Python 5 or Python 6.

Hmmm... When I was hearing the repeated belated saying that Python will
never ever jump
on the statically typed ship on each and every static type annotation
discussion I started to
worry this wasn't indeed the case (why the urge of repeating it so much
otherwise?).

Now we got standard library features requiring type annotation and a little
shift
towards a "not now" position.

I'm just wondering... I'm NOT saying this would be bad (or good).


On Fri, Apr 27, 2018 at 2:36 AM, Steven D'Aprano <steve at pearwood.info>
wrote:

> Hi Fatty, and welcome!
>
> On Thu, Apr 26, 2018 at 08:00:55PM +0200, Fatty Morgan wrote:
>
> > The natural interpretation of 'name := expr' is a PEP 526
> > type-annotated variable initialization 'name : T = expr' with the
> > type annotation T omitted, the tokens ':' and '=' coalesced, and
> > the implied type T inferred as 'type(expr)'.
>
> I'm not sure why you say that is the "natural" interpretation,
> unless you're saying that Guido, Chris, myself and dozens of other
> people taking part of this conversation are unnatural, since none of us
> thought of that interpretation *smiles*
>
> The := token is the second most common assignment operator in
> programming languages, behind only = single equals sign. For those of us
> who were raised on Pascal, it is entirely natural to use = for equality
> tests and := for assignment, and languages that use == for equality are
> the ones which are weird.
>
> Since type-annotations are still only used by a small proportion of
> Python code and Python developers, I doubt that they will jump to the
> interpretation of "explicit type hint with no type given".
>
> If the type-checker can infer the type of the expression, there's no
> need to use the colon at all.
>
>     name := expression  # can infer type here
>     name = expression  # why not just infer the type here?
>
> So using : Type without the type is entirely unnecessary. The colon is
> only needed when you have to specify a type manually.
>
> Your comments about some entirely hypothetical "Python with enforced
> static typing" are interesting but so blue-sky that I honestly doubt
> that there's any point in discussing them now. We're focused on Python
> 3.8 and 3.9, not Python 5 or Python 6.
>
>
> --
> Steve
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