# [Python-checkins] r79920 - python/trunk/Doc/library/itertools.rst

raymond.hettinger python-checkins at python.org
Sat Apr 10 09:01:32 CEST 2010

Author: raymond.hettinger
Date: Sat Apr 10 09:01:32 2010
New Revision: 79920

Log:
Fixup new itertools recipes.

Modified:
python/trunk/Doc/library/itertools.rst

Modified: python/trunk/Doc/library/itertools.rst
==============================================================================
--- python/trunk/Doc/library/itertools.rst	(original)
+++ python/trunk/Doc/library/itertools.rst	Sat Apr 10 09:01:32 2010
@@ -796,7 +796,7 @@
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
@@ -805,12 +805,16 @@
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