I have a draft PEP and an implementation of mutable iterators for lists and dicts that supports delete only.
The PEP (Mutable Iterations) and sample code can be found at: http://www.deprince.net/ideas/peps.html Or, you can get the patch from: http://sourceforge.net/tracker/index.php?func=detail&aid=1459011&group_id=5470&atid=305470 There are two questions that I'd like to put before the Python community at large. The first is which of Java's iterator methods we would like to see. I'm using Java's list-iterator as a template - http://java.sun.com/j2se/1.4.2/docs/api/java/util/ListIterator.html Question #1: Pick which you like, and which you think are too non-pythonic. Let me know. At a minimum we need delete, I'd like to see others, but I'd like to get some feedback before adding something that would make everyone recoil. Operation Works with list Works with dict add Yes Unreliably** hasNext Yes Yes hasPrev Yes Yes previous Yes Yes next Already implemented remove Implemented with patch, called delete (see question #3) set Yes Yes only for dict.values() previousIndex Yes Yes nextIndex Yes Yes And not part of Java, but I'd like to ask everyone anyway. current Yes Yes (the item last returned by next/prev) currentIndex Yes Yes (the item index last returned by next/prev) Question #2: What should delete() return? I currently have it returning the iter itself to make it possible to say: value = iter.delete().next() Example: item = i.next() while reject( item ): item = i.delete().next() I fully expect a groundswell of people to say "just return None." Question #3: Delete vs. remove. On the first cut I took some liberties with the naming. A lot of data-structures have a remove method, the semantics are datastructre.remove( offending_item ). Because in the iterator, which item is selected by the iterator state, not parameter, I didn't want to confuse the two, so I called it remove. The idea is remove has to be told what, delete refers to its internal state. Question #4: At first I wanted to implement Java fast-fail semantics, but now I have reservations. It would require a bit of house keeping on each and evert insert. IMHO, even adding as little as "flag=1" is too much for what is likely one of the most commonly used pieces of code in Python. Can I have a show of hands? For? against? Wait and see how bad the performance hit is before deciding? --- ** Python dicts never rehash on delete, but they can and sometimes must on insert. In fact, you often *can't* do more than fixed number of inserts without a mandatory rehash, otherwise you just run out slots. Even if somebody decides that delete should rehash, iters don't use the dict's delete ... why delete by key when we have something better, the slot #? A little housekeeping and the item is gone with no searching and no comparisons. Cheers - Adam DePrince _______________________________________________ Python-3000 mailing list Python-3000@python.org http://mail.python.org/mailman/listinfo/python-3000 Unsubscribe: http://mail.python.org/mailman/options/python-3000/archive%40mail-archive.com
