Update itertools recipe for consume().

1 files changed, 7 insertions, 1 deletions

diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 4f82a27..f83e976 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -672,7 +672,13 @@ which incur interpreter overhead.
 
    def consume(iterator, n):
        "Advance the iterator n-steps ahead. If n is none, consume entirely."
-       collections.deque(islice(iterator, n), maxlen=0)
+       # Use functions that consume iterators at C speed.
+       if n is None:
+           # feed the entire iterator into a zero-length deque
+           collections.deque(iterator, maxlen=0)
+       else:
+           # advance to the emtpy slice starting at position n
+           next(islice(iterator, n, n), None)
 
    def nth(iterable, n, default=None):
        "Returns the nth item or a default value"