[Python-Dev] Product iteration

[Eric S. Raymond]

Andrew Kuchling <akuchlin@mems-exchange.org>:
> On Tue, Jul 25, 2000 at 03:28:32PM -0400, Eric S. Raymond wrote:
> >[x**2 for x in filter(isprime, range(1, 99)]
>   ...
> >filter, zip, product, and lambda are good enough to cover anything the
> >presently proposed comprehension syntax can handle. 
> 
> ... but not so elegantly, if the filter needs variables from the
> current scope.  Consider removing all numbers in that range that are a
> multiple of a variable 'n'; you'd have to write:
> 
> [x**2 for x in filter(lambda x, number = n: (x%n)!=0, range(1,99)) ]
> 
> This uses the default argument hack to pass the value of 'n' into the
> scope of the lambda-created function as the parameter 'number'.
> Icky... I'd rather see extra syntax than more use of this kludge!

Wrong answer.  The right answer is to fix lambda (or some variant of lambda)
to be a true  lexical closure.
-- 
		<a href="http://www.tuxedo.org/~esr">Eric S. Raymond</a>

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