From da176eeb6862abed5632439c68798aa0e06457e1 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sat, 10 Apr 2010 06:51:41 +0000 Subject: [PATCH] Fixup new itertools recipes. --- Doc/library/itertools.rst | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index dafeeb15371..7156a23a74b 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -784,7 +784,7 @@ which incur interpreter overhead. pools = map(tuple, args) * kwds.get('repeat', 1) return tuple(random.choice(pool) for pool in pools) - def random_permuation(iterable, r=None): + def random_permutation(iterable, r=None): "Random selection from itertools.permutations(iterable, r)" pool = tuple(iterable) r = len(pool) if r is None else r @@ -793,12 +793,16 @@ which incur interpreter overhead. def random_combination(iterable, r): "Random selection from itertools.combinations(iterable, r)" pool = tuple(iterable) - return tuple(sorted(random.sample(pool, r), key=pool.index)) + n = len(pool) + indices = sorted(random.sample(xrange(n), r)) + return tuple(pool[i] for i in indices) def random_combination_with_replacement(iterable, r): "Random selection from itertools.combinations_with_replacement(iterable, r)" pool = tuple(iterable) - return tuple(sorted(imap(random.choice, [pool]*r), key=pool.index)) + n = len(pool) + indices = sorted(random.randrange(n) for i in xrange(r)) + return tuple(pool[i] for i in indices) Note, many of the above recipes can be optimized by replacing global lookups with local variables defined as default values. For example, the