This is a very good summary of the two iterator protocols. Ping, would you mind adding this to PEP 234?
And i thought it was a critique. Fascinating, Captain. :)
I'm happy to add the text, but i want to be clear, then: is it acceptable to write an iterator that only provides <next> if you only care about the "iteration protocol" and not the "for-able protocol"?
No, an iterator ought to provide both, but it's good to recognize that there *are* two protocols.
I see that "ought to" is the most opinion the PEP is willing to give on the topic:
A class is a valid iterator object when it defines a next() method that behaves as described above. A class that wants to be an iterator also ought to implement __iter__() returning itself.
I would like to see this strengthened. I envision "iterator algebra" code that really needs to be able to do a for loop over an iterator when it feels like it. --Guido van Rossum (home page: http://www.python.org/~guido/)