From 7b3debcbd7ad3546049338f5af3f652480422e6a Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Wed, 31 Dec 2008 04:33:06 +0000 Subject: [PATCH] Issue 4790: Eliminate unnecessary work from heapq's nlargest() and nsmallest() functions for the common case where no key function is specified. --- Lib/heapq.py | 14 ++++++++++---- Misc/NEWS | 3 +++ 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/Lib/heapq.py b/Lib/heapq.py index 380fe1268bf8..2d3404644aa4 100644 --- a/Lib/heapq.py +++ b/Lib/heapq.py @@ -354,9 +354,12 @@ def nsmallest(n, iterable, key=None): 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 @@ def nlargest(n, iterable, key=None): 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 diff --git a/Misc/NEWS b/Misc/NEWS index 634fc91eb360..7c8a79377791 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -45,6 +45,9 @@ Core and Builtins 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. -- 2.47.3