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Fixup new itertools recipes.

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Raymond Hettinger 2010-04-10 07:08:41 +00:00
parent d59ceb5b7c
commit 2fc70f05bc
1 changed files with 7 additions and 3 deletions
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10
Doc/library/itertools.rst
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@ -709,7 +709,7 @@ which incur interpreter overhead.
pools = [tuple(pool) for pool in args] * repeat pools = [tuple(pool) for pool in args] * repeat
return tuple(random.choice(pool) for pool in pools) 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)" "Random selection from itertools.permutations(iterable, r)"
pool = tuple(iterable) pool = tuple(iterable)
r = len(pool) if r is None else r r = len(pool) if r is None else r
@ -718,12 +718,16 @@ which incur interpreter overhead.
def random_combination(iterable, r): def random_combination(iterable, r):
"Random selection from itertools.combinations(iterable, r)" "Random selection from itertools.combinations(iterable, r)"
pool = tuple(iterable) pool = tuple(iterable)
return tuple(sorted(random.sample(pool, r), key=pool.index)) n = len(pool)
indices = sorted(random.sample(range(n), r))
return tuple(pool[i] for i in indices)
def random_combination_with_replacement(iterable, r): def random_combination_with_replacement(iterable, r):
"Random selection from itertools.combinations_with_replacement(iterable, r)" "Random selection from itertools.combinations_with_replacement(iterable, r)"
pool = tuple(iterable) pool = tuple(iterable)
return tuple(sorted(map(random.choice, repeat(pool, r)), key=pool.index)) n = len(pool)
indices = sorted(random.randrange(n) for i in range(r))
return tuple(pool[i] for i in indices)
Note, many of the above recipes can be optimized by replacing global lookups Note, many of the above recipes can be optimized by replacing global lookups
with local variables defined as default values. For example, the with local variables defined as default values. For example, the