Simplify explanation of multiset operations by removing restrictions on negative inputs.

1 files changed, 2 insertions, 2 deletions

diff --git a/Lib/collections.py b/Lib/collections.py
index a853076cb2..eb13f4d2fd 100644
--- a/Lib/collections.py
+++ b/Lib/collections.py
@@ -312,8 +312,8 @@ class Counter(dict):
         if not isinstance(other, Counter):
             return NotImplemented
         result = Counter()
-        for elem, count in self.iteritems():
-            newcount = count - other[elem]
+        for elem in set(self) | set(other):
+            newcount = self[elem] - other[elem]
             if newcount > 0:
                 result[elem] = newcount
         return result