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As Robert noted, the map() and filter() builtins in Python 3 are already lazy and there's no reason to expand the iterator protocol for this functionality.
Map and filter also have dedicated syntax in the form of comprehensions and generator expressions:
 itr = (x for x in map(abs, range(10)) if x % 5 == 0)
Furthermore, the standard library already provides an entire module of tools for creating and working with lazy iterators in both Python 2 and Python 3: http://docs.python.org/library/itertools