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

[Antoine Pitrou]

On Thu, 26 Apr 2018 08:38:51 +1000
Chris Angelico <rosuav at gmail.com> wrote:

> On Thu, Apr 26, 2018 at 8:08 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > On Wed, 25 Apr 2018 16:55:43 -0500
> > Tim Peters <tim.peters at gmail.com> wrote:  
> >>
> >> To my eyes, this is genuinely harder to follow, despite its relative brevity:
> >>
> >>         while total != (total := total + term):  
> >
> > Does it even work?  Perhaps if the goal is to stop when total is NaN,
> > but otherwise?  
> 
> Yes, it does, because the first "total" is looked up before the
> rebinding happens. It's 100% unambiguous to the compiler... but still
> pretty unclear to a human. And I think the multiple use of 'total' is
> to blame for that. So I agree with Tim that this particular example is
> better in longhand.

"Better" is an understatement :-(  Now that I understood it (thanks
for the explanation), the shorthand version appears completely bonkers.

Regards

Antoine.