Issue 7764: Improve recipe for itertools.consume().

This commit is contained in:
Raymond Hettinger 2010-01-24 03:34:56 +00:00
parent 495517cd38
commit cef40c34a9
1 changed files with 14 additions and 1 deletions

View File

@ -641,7 +641,13 @@ 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)
# 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 @@ which incur interpreter overhead.
# 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))