grocery_stocker wrote: > Give the following code.. > >>>> class it: > ... def __init__(self): > ... self.count = -1 > ... def next(self): > ... self.count +=1 > ... if self.count < 4: > ... return self.count > ... else: > ... raise StopIteration > ... >>>> def some_func(): > ... return it()
this creates a new instance of "it", with a new count, every time the function is called. >>>> iterator = some_func() this sets iterator to be an instance of "it". >>>> iterator > <__main__.it instance at 0xb7f482ac> this is the single "it" instance that iterator is bound to. >>>> some_func > <function some_func at 0xb7f45e64> >>>> some_func() > <__main__.it instance at 0xb7f4862c> this is another instance of "it" created when some_func was called. > How come when I call some_func().next(), the counter doesn't get > incremented? >>>> some_func().next() > 0 this creates yet another instance of "it" and calls next() on it. >>>> some_func().next() > 0 this creates another instance of "it" and calls next() on it. >>>> some_func().next() > 0 and another instance.... > But when I call iterator.next(), it does. >>>> iterator.next() > 0 this calls next() on the instance of "it" that iterator is bound to. >>>> iterator.next() > 1 this call next() again on the same instance of "it". >>>> iterator.next() > 2 >>>> iterator.next() > 3 in summary: iterator is bound to one instance of "it", while some_func() returns a new instance each time it is called. BUT while what you are doing is interesting, it is not the same as Python's iterators, which use "yield" from a function and don't require storing a value in a class. look for "yield" in the python docs. this comment may be irrelevant; i am just worried you are confusing the above (which apart from the mistake about instances is perfectly ok) and python's iterators (which use next(), yield, etc). andrew -- http://mail.python.org/mailman/listinfo/python-list
