I would like to leave this as-is.  Consistency between error message wording is one of our least important considerations.  The __getitem__ message is somewhat useful -- it helps learners know which magic method is being called and what they would need to add to a class to make it work.  This was the typical wording for old-style classes.  For example, calling len() on an old-style class without __len__ gave this message, "AttributeError: A instance has no attribute '__len__'".

In addition, we are getting very close to end-of-life for Python2.7.  Accordingly, any changes at this point should be limited to things that really matter.  It will be too easy to introduce a new problem that we won't have an opportunity to fix later.

I recommend closing this and shifting attention to things that matter.