No need to register classes that already inherit from ABCs.

Lib/UserList.py

@@ -85,5 +85,3 @@ class UserList(collections.MutableSequence):
             self.data.extend(other.data)
         else:
             self.data.extend(other)
-
-collections.MutableSequence.register(UserList)

Lib/UserString.py

@@ -214,8 +214,6 @@ class MutableString(UserString, collections.MutableSequence):
     def insert(self, index, value):
         self[index:index] = value
 
-collections.MutableSequence.register(MutableString)
-
 if __name__ == "__main__":
     # execute the regression test to stdout, if called as a script:
     import os