On Mon, 02 Nov 2009 19:19:41 +1100, Ben Finney wrote: > "Jon P." <jbpe...@gmail.com> writes: > >> I'd like to do: >> >> resultlist = operandlist1 + operandlist2 > > That's an unfortunate way of expressing it; it's valid Python syntax > that doesn't do what you're describing (in this case, it will bind > ‘resultlist’ to a new list that is the *concatenation* of the two > original lists).
True, but it is valid mathematical syntax if you interpret lists as vectors. I'm sure there are languages where [1,2]+[3,4] will return [4,6]. Possibly R or Mathematica? > Yes, just about any ‘map()’ operation has a corresponding list > comprehension. (Does anyone know of a counter-example, a ‘map()’ > operation that doesn't have a correspondingly simple list > comprehension?) Everyone forgets the multiple argument form of map. map(func, s1, s2, s3, ...) would need to be written as: [func(t) for f in itertools.izip_longest(s1, s2, s3, ...)] which I guess is relatively simple, but only because izip_longest() does the hard work. On the other hand, list comps using an if clause can't be written as pure maps. You can do this: [func(x) for x in seq if cond(x)] filter(cond, map(func, seq)) but the second version may use much more temporary memory if seq is huge and cond very rarely true. And I don't think you could write this as a single map: [func(a, b) for a in seq1 for b in seq2] -- Steven -- http://mail.python.org/mailman/listinfo/python-list
