[Python-ideas] Accessing the result of comprehension's expression from the conditional
Arnaud Delobelle
arnodel at googlemail.com
Fri Jun 19 21:12:51 CEST 2009
On 18 Jun 2009, at 21:19, Lie Ryan wrote:
> In list/generator comprehension, currently we have no way to access
> the
> result of the expression and have to write something like this:
>
> [f(x) for x in l if f(x) > 0]
>
> if f() is heavy or non-pure (i.e. have side effects), calling f()
> twice
> might be undesirable.
>
> Even if f() is not a function such as
>
> [x + 1 for x in l if x + 1 > 0]
>
> it looks ugly since we're repeating ourself.
>
> We can work around it like this:
>
> [y for y in (f(x) for x in l) if y > 0]
>
> but then we have an unnecessary nested loop comprehension
You can write:
[y for x in l for y in [f(x)] if y > 0]
Which is even worse ;)
--
Arnaud
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