[Tutor] Iterators and Generators...

[Karl Pflästerer]

On 13 Aug 2003, Marc Barry <- marc_barry at hotmail.com wrote:

> class list_iterator:

> 	def __init__(self, a_list):
> 		self.a_list = a_list

> 	def __iter__(self):
> 		return self
                           ^^^^
here you should call your next method

> 	def next(self):
> 		for i in self.a_list:
> 			yield i
> 		raise StopItertion
                             ^^
StopIteration

> a_list_iterator = list_iterator([1,2,3,4,5,6,7,8,9,10])

> for i in a_list_iterator:
> 	print i

[...]
> Instead, I get something similar to the following:

> <generator object at 0x007EA328>
[...]

> ...  Well you get the point, it just loops forever.  Also, my yeild
> statement seems to be retruning a generator object instead of the
> number.  Also, it never reaches the 'raise' statement.  Obviously,
> there is a flaw in my understanding of how to use a generator and the
> iterator protocol.  Can anyone clear this up for me?

You never called your next() method (and you have a typo); I underlined
both in your example.

So the correct code would be:

class list_iterator:
        def __init__(self, a_list):
                self.a_list = a_list

        def __iter__(self):
                return self.next()

        def next(self):
                for i in self.a_list:
                        yield i
                raise StopIteration

# Example in IPython
In [32]: a_list_iterator = list_iterator([1,2,3,4,5,6,7,8,9,10])

In [33]: for i in a_list_iterator:
   ....:     print i
   ....: 
1
2
3
4
5
6
7
8
9
10


   Karl
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