On page 406 of Section 10.1.3, we give an implementation of the method setdefault as it might appear in the MutableMapping abstract base class. While that method accomplishes the goal in a general fashion, its efficiency is less than ideal. In particular, when the key is new, there will be a failed search due to the initial use of _ _getitem_ _, and then a subsequent insertion via _ _setitem_ _. For a concrete implementation, such as the UnsortedTableMap, this is twice the work because a complete scan of the table will take place during the failed _ _getitem_ _, and then another complete scan of the table takes place due to the implementation of _ _setitem_ _. A better solution is for the UnsortedTableMap class to override setdefault to provide a direct solution that performs a single search. Give such an implementation of UnsortedTableMap.setdefault.