Hi: Thanks, it does help. Besides, I search the web and find several other examples, too. --Thomas
----- Original Message ----- From: "Fredrik Lundh" <[EMAIL PROTECTED]> To: <python-list@python.org> Sent: Wednesday, November 16, 2005 4:02 PM Subject: Re: Is there any Iterator type example? > Thomas Moore wrote: > > > But what I really want to know is how to use __iter()__ and next() in a > > class with an example. > > here's a simple iterator class that iterators over itself once: > > class Iterator1: > def __init__(self, size=10): > self.count = 0 > self.size = size > def __iter__(self): > return self > def next(self): > count = self.count + 1 > if count >= self.size: > raise StopIteration > self.count = count > return count > > it = Iterator1() > print it > for i in it: > print i > for i in it: > print i > > if you run this, you'll see that only the first for-statement will actually > print anything. when you loop over the iterator again, it's already ex- > hausted. > > here's a more general variant, where the Iterable class can be iterated > over several times. to do this, its __iter__ method uses a separate helper > class to do the actual iteration: > > class Iterable2: > def __init__(self, size=10): > self.size = size > def __iter__(self): > return Iterator2(self) > > class Iterator2: > def __init__(self, target): > self.target = target > self.count = 0 > def __iter__(self): > return self > def next(self): > count = self.count + 1 > if count >= self.target.size: > raise StopIteration > self.count = count > return count > > it = Iterable2() > print it > for i in it: > print i > for i in it: > print i > > to get a better view of what happens when you run the code, try adding > print statements to the __iter__ and next methods. > > hope this helps! > > </F> > > > > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
