Maybe the reasons behind having __iter__() returning itself should be clearly expressed in the PEP, too. On this list, Tim gave one recently, Guido gives another here, but unless I missed it, the PEP gives none. Usually, PEPs explain the reasons behind the choices.
Ping added this to the PEP: The two methods correspond to two distinct protocols: 1. An object can be iterated over with "for" if it implements __iter__() or __getitem__(). 2. An object can function as an iterator if it implements next(). Container-like objects usually support protocol 1. Iterators are currently required to support both protocols. The semantics of iteration come only from protocol 2; protocol 1 is present to make iterators behave like sequences. But the analogy is weak -- unlike ordinary sequences, iterators are "sequences" that are destroyed by the act of looking at their elements. (I could do without the last sentence, since this expresses a value judgement rather than fact -- not a good thing to have in a PEP's "specification" section.) --Guido van Rossum (home page: http://www.python.org/~guido/)