On Fri, 2009-05-22 at 10:54 -0700, Jan wrote: > On May 22, 9:46 am, "J. Cliff Dyer" <j...@sdf.lonestar.org> wrote: > > > You don't need a reset method. There is no hard and fast rule that > > __iter__ must return the object itself. It just needs to return an > > iterator. > > I disagree. > If ITRATOR is a true iterator, ITRATOR.__iter__() must return > ITERATOR. > If ITERABLE is an iterable (but not necessarily an iterator) > ITRABLE.__iter__() must return an iterator. >
You are correct: It is an iterable, not an iterator. However, that's not a disagreement with me. It may not be an iterator (and I probably should have said so) but it works, and it solves the OP's problem. > > For example: > > > > >>> l = [1,2,3] > > >>> l.__iter__() > > > > <listiterator object at 0x7fd0da315850>>>> l is l.__iter__() > > > > False > > [1,2,3] is an iterable but not an iterator, so this False result is > expected. > Compare this with the following. > > >>> ii = iter([1,2,3]) # ii is an iterator. > >>> next(ii) > 1 > >>> jj = ii.__iter__() # call __iter__ method on an iterator > >>> ii is jj > True > >>> next(jj) > 2 > > > Just create a class with an __iter__ method that returns a reset > > iterator object. > > > > class X(object): > > def __init__(self, max=3): > > self.counter = 0 > > self.max = max > > def __iter__(self): > > return self > > def next(self): > > if self.counter < self.max: > > self.counter += 1 > > return self.counter > > else: > > raise StopIteration > > > > class Y(object): > > def __iter__(self): > > return X() > > > > In this setup, X has the problem you are trying to avoid, but Y behaves > > as a resettable iterable. > > > y = Y() > > This does not work. > > With this, y is not an interator, and not even an iterable. > > > for c in y: > > This produces an error because by definition of for-loops > it is executed the same way as: > > temp_iterator = iter(y) # temp_iterator is y > while True: > try: > print(next(temp_iterator)) # temp_iterator does not support > __next__() > except StopIteration: > break > Did you try running my code? I did. It works on my computer. What error message did you get? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
