The default argument in dict.setdefault() defaults to None.

Add this default to UserDict.DictMixin.setdefault() too.

diff --git a/Lib/UserDict.py b/Lib/UserDict.py
index 87cc6a35a96c74f7ce17df024aebd9acdf5c0fde..703f118a428709c69d7b9a485ef378fa5f4af69a 100644 (file)
--- a/Lib/UserDict.py
+++ b/Lib/UserDict.py
@@ -113,7 +113,7 @@ class DictMixin:
     def clear(self):
         for key in self.keys():
             del self[key]
-    def setdefault(self, key, default):
+    def setdefault(self, key, default=None):
         try:
             return self[key]
         except KeyError: