[Python-ideas] Introducing where clauses
Andrey Popp
8mayday at gmail.com
Mon Jun 22 14:46:44 CEST 2009
I think that producing a list of tuples (that is conceptually image of
mapping from some_iterable set) is basic operation.
But... ok, now we have three ways to produce list below:
[(f(x), f(x)) for x in some_iterable if f(x) < 2]
1)
> def g(iterable):
> for x in iterable:
> y = f(x)
> if y < 2:
> yield (y, y)
2)
> [(y, y) for y in (f(x) for x in some_iterable) if y < 2]
3)
> map(lambda obj: (obj, obj),
> filter(lambda y: y < 2,
> map(f, some_iterable)))
And none of them does not look as obvious as
[(f(x), f(x)) for x in some_iterable if f(x) < 2]
, doesn't it? While proposed variant with where-clause
[(y, y) for x in some_iterable if y < 2 where y = f(x)]
looks more naturally than three suggested variants.
I give strong emphasis on that fact, that where-clause is only
syntactic sugar, suggested for better readability.
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