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

Rob Cliffe rob.cliffe at btinternet.com
Mon Jul 2 17:46:56 EDT 2018

On 02/07/2018 19:19, Guido van Rossum wrote:
> Thank you all. I will accept the PEP as is. I am happy to accept 
> *clarification* updates to the PEP if people care to submit them as 
> PRs to the peps repo (https://github.com/python/peps), and that could 
> even (to some extent) include summaries of discussion we've had, or 
> outright rejected ideas. But even without any of those I think the PEP 
> is very clear so I will not wait very long (maybe a week).
It's late to raise this, but what exactly are the objections to the syntax
         expr -> name  # or variations such as  expr => name
instead of
         name := expr

The PEP mentions that this syntax does not have a problem that "as" 
does, but does not list any downsides of it.
It conforms to left-to-right evaluation, where name:=expr does not.
It (I would argue) reduces the asymmetry of the first use of a 
sub-expression in cases such as
     [ ( (f(x) -> y)**2, y**3, y**4) for x in iterable ]
     [ ( (y := f(x))**2, y**3, y**4) for x in iterable ]
because the first "y" is closer to the way it is used, viz "**2".

Rob Cliffe

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