From: Raymond Hettinger <python@rcn.com>
Date: Tue, 26 May 2015 17:35:15 +0000 (-0700)
Subject: Issue #23509: Speed up Counter operators
X-Git-Tag: v3.5.0b2~13^2~36
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=944db38cb720b511aad5d7850dec71402e7e2725;p=thirdparty%2FPython%2Fcpython.git

Issue #23509: Speed up Counter operators
(Based on patch by Serhiy Storchaka.)
---

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index fc60e13daad0..9c22d86d7980 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -736,14 +736,22 @@ class Counter(dict):
 
     def __pos__(self):
         'Adds an empty counter, effectively stripping negative and zero counts'
-        return self + Counter()
+        result = Counter()
+        for elem, count in self.items():
+            if count > 0:
+                result[elem] = count
+        return result
 
     def __neg__(self):
         '''Subtracts from an empty counter.  Strips positive and zero counts,
         and flips the sign on negative counts.
 
         '''
-        return Counter() - self
+        result = Counter()
+        for elem, count in self.items():
+            if count < 0:
+                result[elem] = 0 - count
+        return result
 
     def _keep_positive(self):
         '''Internal method to strip elements with a negative or zero count'''