[Python-Dev] Informal educator feedback on PEP 572 (was Re: 2018 Python Language Summit coverage, last part)

Steven D'Aprano steve at pearwood.info
Sat Jun 30 05:58:47 EDT 2018

On Sat, Jun 30, 2018 at 06:30:56PM +1000, Nick Coghlan wrote:

> The significant semantic differences between "{x : 1}" and "{x := 1}"
> are also rather surprising :)

*Significant* and obvious differences are good. It's the subtle 
differences that you don't notice immediately that really hurt:

    {x+1} versus {x-1}
    x > y versus x < y
    x/y versus x//y

    alist = [a, b]
    alist = (a, b)

Sometimes small differences in punctuation or spelling make a big 
difference to semantics.

    Punctuation Saves Lives!

    "Let's eat, grandma!"

    "Let's eat grandma!"

Unless you propose to ban all operators and insist on a minimum string 
distance between all identifiers:


picking out little differences in functionality caused by little 
differences in code is a game we could play all day.

At least we won't have the "=" versus "==" bug magnet from C, or the 
"==" versus "===" confusion from Javascript. Compared to that, the 
in-your-face obvious consequences of {x: 1} versus {x := 1} are pretty 


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