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>
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