[Python-ideas] Introducing where clauses
jimjjewett at gmail.com
Mon Jun 22 14:59:51 CEST 2009
On Mon, Jun 22, 2009 at 8:46 AM, Andrey Popp<8mayday at gmail.com> wrote:
> [(y, y) for x in some_iterable if y < 2 where y = f(x)]
> looks more naturally than three suggested variants.
Only if you are already thinking about SQL.
An "as" would be almost as good as a "where", and would better match
the way python has evolved so far.
But that still doesn't answer the real question. In isolation, I
would see either as a real (if perhaps small and isolated) improvement
The catch is that the improvement must be dramatic enough to justify
the cost -- which is extra complexity to the language as a whole.
That isn't a cost you see as easily, because you're thinking about
comprehensions; it is instead a small tax paid by people doing regular
function calls and if branching and for loops. It isn't a big tax,
but it is cumulative, and python has worked hard to minimize it.
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