Add support for unary plus and unary minus to collections.Counter()

1 files changed, 11 insertions, 0 deletions

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index 03bd2b3..2007e68 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -672,6 +672,17 @@ class Counter(dict):
                 result[elem] = newcount
         return result
 
+    def __pos__(self):
+        'Adds an empty counter, effectively stripping negative and zero counts'
+        return self + Counter()
+
+    def __neg__(self):
+        '''Subtracts from an empty counter.  Strips positive and zero counts,
+        and flips the sign on negative counts.
+
+        '''
+        return Counter() - self
+
 
 ########################################################################
 ###  ChainMap (helper for configparser and string.Template)