[Python-Dev] (name := expression) doesn't fit the narrative of PEP 20

[Terry Reedy]

On 4/26/2018 6:20 AM, Steve Holden wrote:
> On Thu, Apr 26, 2018 at 8:56 AM, Steven D'Aprano <steve at pearwood.info 
> <mailto:steve at pearwood.info>> wrote:
> 
>     On Thu, Apr 26, 2018 at 03:31:13AM -0400, Terry Reedy wrote:
>     > On 4/25/2018 8:20 PM, Chris Angelico wrote:
>     > >On Thu, Apr 26, 2018 at 10:11 AM, Yury Selivanov
>     > ><yselivanov.ml at gmail.com <mailto:yselivanov.ml at gmail.com>> wrote:
>     > >>Just yesterday this snippet was used on python-dev to show how great the
>     > >>new syntax is:
>     > >>
>     > >>           my_func(arg, buffer=(buf := [None]*get_size()), size=len(buf))
>     > 
>     > What strikes me as awful about this example is that len(buf) is 
>     > get_size(), so the wrong value is being named and saved. 
>     > 'size=len(buf)' is, in a sense, backwards.
> 
>     Terry is absolutely right, and I'm to blame for that atrocity. Mea
>     culpa.
> 
> ​Perhaps a better spelling would be
> 
>      my_func(arg, buffer=[None]*(buflen := get_size()), size=buflen)

That is exactly what I wrote in the continuation that Steven snipped.

-- 
Terry Jan Reedy