Issue 7764: Improve recipe for itertools.consume().
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index 229bc1f..250c842 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -641,7 +641,13 @@
def consume(iterator, n):
"Advance the iterator n-steps ahead. If n is none, consume entirely."
- collections.deque(islice(iterator, n), maxlen=0)
+ # The technique uses objects 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"
@@ -751,3 +757,10 @@
# unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
# unique_justseen('ABBCcAD', str.lower) --> A B C A D
return imap(next, imap(itemgetter(1), groupby(iterable, key)))
+
+Note, many of the above recipes can be optimized by replacing global lookups
+with local variables defined as default values. For example, the
+*dotproduct* recipe can be written as:
+
+ def dotproduct(vec1, vec2, sum=sum, imap=imap, mul=operator.mul):
+ return sum(imap(mul, vec1, vec2))