[Python-ideas] filter-only list comps
stefan_ml at behnel.de
Fri Feb 26 14:47:38 CET 2010
Stephen J. Turnbull, 26.02.2010 04:28:
> Greg Ewing writes:
> > [x from stuff]
> > is a shorthand for
> > [x for x in stuff]
> Any time you say "shorthand" you're probably violating TOOWTDI. :-)
Absolutely, so I would expect this to have zero change to make it in.
> > As a bonus, the short form could probably be made more
> > efficient, because the tuples produced by the for-loop
> > could be put straight into the result list, instead of
> > having to re-pack k and v into a new tuple.
> This is a straightforward optimization that should be done anyway,
> though, if it isn't done already.
That's a good idea. Note, however, that the item extracted from the
iterable is not necessarily a tuple:
>>> l = [[1,2], [3,4]]
>>> [ (x,y) for (x,y) in l]
[(1, 2), (3, 4)]
So the tuple packing may or may not be required, but that can only be
decided at runtime.
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