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[Python-ideas] Assignments in list/generator expressions

Nick Coghlan ncoghlan at gmail.com
Tue Apr 12 01:49:12 CEST 2011 
On Tue, Apr 12, 2011 at 9:17 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Nick Coghlan wrote:
>
>> ys = [y for x in xs given f(x) as y if y]
>
> Hmmm. Here I find myself getting tripped up by the ordering
> when I try to read that smoothly.
>
> I think it's because words like 'given' or 'where', as used
> in mathematics, imply a definition of something that's been
> used *before*, whereas here it's defining something to be
> used *after* (i.e. in the following 'if' clause).

This one is tricky, since the assignment is *after* the for loop, but
*before* the filter condition.

You could reorder it as below, but the translation to long-form Python
code wouldn't be quite as clean (since the order of clauses wouldn't
follow the order of nesting any more).

ys = [y for x in xs if y given f(x) as y]

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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