Merged revisions 68546 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r68546 | raymond.hettinger | 2009-01-12 04:37:32 -0600 (Mon, 12 Jan 2009) | 1 line
Optimize heapq.nsmallest/nlargest for cases where n==1 or n>=size.
........
diff --git a/Lib/heapq.py b/Lib/heapq.py
index 2d34046..24997bf 100644
--- a/Lib/heapq.py
+++ b/Lib/heapq.py
@@ -129,7 +129,7 @@
__all__ = ['heappush', 'heappop', 'heapify', 'heapreplace', 'merge',
'nlargest', 'nsmallest', 'heappushpop']
-from itertools import islice, repeat, count, tee
+from itertools import islice, repeat, count, tee, chain
from operator import itemgetter, neg
import bisect
@@ -354,10 +354,32 @@
Equivalent to: sorted(iterable, key=key)[:n]
"""
+ # Short-cut for n==1 is to use min() when len(iterable)>0
+ if n == 1:
+ it = iter(iterable)
+ head = list(islice(it, 1))
+ if not head:
+ return []
+ if key is None:
+ return [min(chain(head, it))]
+ return [min(chain(head, it), key=key)]
+
+ # When n>=size, it's faster to use sort()
+ try:
+ size = len(iterable)
+ except (TypeError, AttributeError):
+ pass
+ else:
+ if n >= size:
+ return sorted(iterable, key=key)[:n]
+
+ # When key is none, use simpler decoration
if key is None:
it = zip(iterable, count()) # decorate
result = _nsmallest(n, it)
return list(map(itemgetter(0), result)) # undecorate
+
+ # General case, slowest method
in1, in2 = tee(iterable)
it = zip(map(key, in1), count(), in2) # decorate
result = _nsmallest(n, it)
@@ -369,10 +391,33 @@
Equivalent to: sorted(iterable, key=key, reverse=True)[:n]
"""
+
+ # Short-cut for n==1 is to use max() when len(iterable)>0
+ if n == 1:
+ it = iter(iterable)
+ head = list(islice(it, 1))
+ if not head:
+ return []
+ if key is None:
+ return [max(chain(head, it))]
+ return [max(chain(head, it), key=key)]
+
+ # When n>=size, it's faster to use sort()
+ try:
+ size = len(iterable)
+ except (TypeError, AttributeError):
+ pass
+ else:
+ if n >= size:
+ return sorted(iterable, key=key, reverse=True)[:n]
+
+ # When key is none, use simpler decoration
if key is None:
it = zip(iterable, map(neg, count())) # decorate
result = _nlargest(n, it)
return list(map(itemgetter(0), result)) # undecorate
+
+ # General case, slowest method
in1, in2 = tee(iterable)
it = zip(map(key, in1), map(neg, count()), in2) # decorate
result = _nlargest(n, it)