MutableSequence requires an insert() method.

diff --git a/Lib/UserString.py b/Lib/UserString.py
index 615c135f164576706b329b8df68de98326184ca1..c3267ad73331496e88e7205056b30967b08e512e 100755 (executable)
--- a/Lib/UserString.py
+++ b/Lib/UserString.py
@@ -232,6 +232,8 @@ class MutableString(UserString, collections.MutableSequence):
     def __imul__(self, n):
         self.data *= n
         return self
+    def insert(self, index, value):
+        self[index:index] = value
 
 collections.MutableSequence.register(MutableString)