On Sun, 17 May 2009 18:24:34 +0200, Diez B. Roggisch wrote: >> But reduce()? I can't see how you can parallelize reduce(). By its >> nature, it has to run sequentially: it can't operate on the nth item >> until it is operated on the (n-1)th item. > > That depends on the operation in question. Addition for example would > work.
You'd think so, but you'd be wrong. You can't assume addition is always commutative. >>> reduce(operator.add, (1.0, 1e57, -1e57)) 0.0 >>> reduce(operator.add, (1e57, -1e57, 1.0)) 1.0 > My math-skills are a bit too rusty to qualify the exact nature of > the operation, commutativity springs to my mind. And how is reduce() supposed to know whether or not some arbitrary function is commutative? -- Steven -- http://mail.python.org/mailman/listinfo/python-list
