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None of the existing iterators (incl dicts, lists, tuples, and 
files) use __getitem__.  Most likely, user defined iterators 
also access the data structure directly (for flexiblity and 
speed). Also, anything that uses PyTuple_GET_ITEM 
bypasses __getitem__.

If string/unicode iterators are added, they should also go
directly to the underlying data; otherwise, there is no point 
to it.

Also, the proposal to change filtertuple(), doesn't solve
inconsistencies within filterstring() which uses __getitem__ 
when there is a function call, but bypasses it when the 
function parameter is Py_None.

I think the right answer is to change filterstring() to use an 
iterator and to implement string/unicode iterators that 
access the data directly (not using __getitem__).

FYI for Tim:  MvL noticed and fixed the unicode vs string 
difference.  His patch, SF #636005, has not been applied 
yet.