From: Raymond Hettinger <python@rcn.com>
Date: Sat, 30 May 2015 05:14:07 +0000 (-0700)
Subject: Issue #23509: Speed up Counter operators
X-Git-Tag: v3.5.0b2~19
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=4c97a62ae34a0e892755a8f95ae6e11881d6feb3;p=python

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 6794de1f8e..80dc4f6d4e 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -753,14 +753,22 @@ 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'''