From dd01f8f37b98af090098495200107dfaf92a3162 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Thu, 22 Jan 2009 09:09:55 +0000 Subject: [PATCH] Update comments and add an optimized path for Counter.update(). --- Lib/collections.py | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/Lib/collections.py b/Lib/collections.py index 232c77258f4..6831cf1396c 100644 --- a/Lib/collections.py +++ b/Lib/collections.py @@ -255,8 +255,11 @@ class Counter(dict): if iterable is not None: if isinstance(iterable, Mapping): - for elem, count in iterable.items(): - self[elem] += count + if self: + for elem, count in iterable.items(): + self[elem] += count + else: + dict.update(self, iterable) # fast path when counter is empty else: for elem in iterable: self[elem] += 1 @@ -282,7 +285,6 @@ class Counter(dict): # Knuth TAOCP Volume II section 4.6.3 exercise 19 # and at http://en.wikipedia.org/wiki/Multiset # - # Results are undefined when inputs contain negative counts. # Outputs guaranteed to only include positive counts. # # To strip negative and zero counts, add-in an empty counter: