Add an example to address a common question of how to split iterators.
diff --git a/Lib/test/test_itertools.py b/Lib/test/test_itertools.py
index 057b576..8ab4cea 100644
--- a/Lib/test/test_itertools.py
+++ b/Lib/test/test_itertools.py
@@ -487,6 +487,9 @@
Walter
Samuele
+>>> def take(n, seq):
+... return list(islice(seq, n))
+
>>> def enumerate(iterable):
... return izip(count(), iterable)
@@ -539,12 +542,26 @@
... result = result[1:] + (elem,)
... yield result
->>> def take(n, seq):
-... return list(islice(seq, n))
+>>> def tee(iterable):
+... "Return two independent iterators from a single iterable"
+... def gen(next, data={}, cnt=[0]):
+... dpop = data.pop
+... for i in count():
+... if i == cnt[0]:
+... item = data[i] = next()
+... cnt[0] += 1
+... else:
+... item = dpop(i)
+... yield item
+... next = iter(iterable).next
+... return (gen(next), gen(next))
This is not part of the examples but it tests to make sure the definitions
perform as purported.
+>>> take(10, count())
+[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+
>>> list(enumerate('abc'))
[(0, 'a'), (1, 'b'), (2, 'c')]
@@ -590,8 +607,17 @@
>>> dotproduct([1,2,3], [4,5,6])
32
->>> take(10, count())
-[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+>>> def irange(start, stop):
+... for i in range(start, stop):
+... yield i
+
+>>> x, y = tee(irange(2,10))
+>>> list(x), list(y)
+([2, 3, 4, 5, 6, 7, 8, 9], [2, 3, 4, 5, 6, 7, 8, 9])
+
+>>> x, y = tee(irange(2,10))
+>>> zip(x, y)
+[(2, 2), (3, 3), (4, 4), (5, 5), (6, 6), (7, 7), (8, 8), (9, 9)]
"""