[Python-checkins] r68096 - in python/branches/release30-maint: Lib/heapq.py Misc/NEWS

[raymond.hettinger]

Author: raymond.hettinger
Date: Wed Dec 31 05:33:06 2008
New Revision: 68096

Log:
Issue 4790:  Eliminate unnecessary work from heapq's nlargest() and nsmallest()
functions for the common case where no key function is specified.



Modified:
   python/branches/release30-maint/Lib/heapq.py
   python/branches/release30-maint/Misc/NEWS

Modified: python/branches/release30-maint/Lib/heapq.py
==============================================================================
--- python/branches/release30-maint/Lib/heapq.py	(original)
+++ python/branches/release30-maint/Lib/heapq.py	Wed Dec 31 05:33:06 2008
@@ -354,9 +354,12 @@
 
     Equivalent to:  sorted(iterable, key=key)[:n]
     """
+    if key is None:
+        it = zip(iterable, count())                         # decorate
+        result = _nsmallest(n, it)
+        return list(map(itemgetter(0), result))             # undecorate
     in1, in2 = tee(iterable)
-    keys = in1 if key is None else map(key, in1)
-    it = zip(keys, count(), in2)                           # decorate
+    it = zip(map(key, in1), count(), in2)                   # decorate
     result = _nsmallest(n, it)
     return list(map(itemgetter(2), result))                 # undecorate
 
@@ -366,9 +369,12 @@
 
     Equivalent to:  sorted(iterable, key=key, reverse=True)[:n]
     """
+    if key is None:
+        it = zip(iterable, map(neg, count()))               # decorate
+        result = _nlargest(n, it)
+        return list(map(itemgetter(0), result))             # undecorate
     in1, in2 = tee(iterable)
-    keys = in1 if key is None else map(key, in1)
-    it = zip(keys, map(neg, count()), in2)                 # decorate
+    it = zip(map(key, in1), map(neg, count()), in2)         # decorate
     result = _nlargest(n, it)
     return list(map(itemgetter(2), result))                 # undecorate
 

Modified: python/branches/release30-maint/Misc/NEWS
==============================================================================
--- python/branches/release30-maint/Misc/NEWS	(original)
+++ python/branches/release30-maint/Misc/NEWS	Wed Dec 31 05:33:06 2008
@@ -45,6 +45,9 @@
 Library
 -------
 
+- Issue 4790: The nsmallest() and nlargest() functions in the heapq module
+  did unnecessary work in the common case where no key function was specified.
+
 - Issue #4702: Throwing a DistutilsPlatformError instead of IOError in case 
   no MSVC compiler is found under Windows. Original patch by Philip Jenvey.