From: Raymond Hettinger <python@rcn.com>
Date: Thu, 22 Jan 2009 09:09:55 +0000 (+0000)
Subject: Update comments and add an optimized path for Counter.update().
X-Git-Tag: v3.1a1~434
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=dd01f8f37b98af090098495200107dfaf92a3162;p=python

Update comments and add an optimized path for Counter.update().
---

diff --git a/Lib/collections.py b/Lib/collections.py
index 232c77258f..6831cf1396 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: