There is just a little more work to do on this.

1) The class level docstrings needs to display which methods are required.  Sequence.__doc__ already does a good job of this but most of the other classes are missing docstrings or don't specific the needed methods.

2) Methods like Sequence.count and Mapping.__eq__ already have a good docstrings but there is nothing for most of the other methods.  The docstring should be modeled on that for the corresponding methods in the concrete classes (list.__getitem__ for example).