iter jitters

[Steven Brent]

OK, thanks ... that explains why my other idea of returning a new list 
to iterate over didn't work either. Talk about chasing one's tail...

Btw, I just realized that a custom __getitem__ method I defined earlier 
in the module(and unhelpfully didnt post), handles the iteration in 2 lines!
	
	def __getitem__(self, index):
         	return self.data[index]

This is the kind of thing I was after, because I didn't want any 
iteration going on in the __iter__ definition itself. Trying to reinvent 
the wheel for exercise.

But generators are cool, and I promise to use them lots :-)

This seems to be a recurring pattern for me; I get deep into confusion 
by skipping over the obvious. Thanks for the clarity and knowledge.

--Steven the newbie

===========================
Diez B. Roggisch wrote:

> Steven Brent wrote:
> 
> 
>>In the snippet below, I'm trying to overload the __iter__ list method:
>>
>>     def __iter__(self):
>>             print "using custom iter"
>>             counter = 0
>>             end = len(self.data) - 1
>>             while counter <= end:
>>                print self.data[counter]
>>                counter += 1
>>
>>It pretty much works, except that the output is ugly when the while loop
>>falls off the end of the list:
>>
> 
> 
>>       File "mylist.py", line 38, in ?
>>         for item in L3:print item,
>>     TypeError: iter() returned non-iterator of type 'NoneType'
>>
>>Oh, yeah, plus it's adding a newline at the end of each item even though
>>I've got the comma there. I'm gonna keep plugging away to see if I can
>>figure this out, but stuff like this makes me frustrated... Thanks a
>>million.
> 
> 
> I think you've got something wrong here - __iter__ is supposed to return an
> object that supports the iteration protocol - mainly a next() method that
> throws an exception when no more elements are available.
> 
> Today, this kind of thingy is usually done using generators:
> 
> class foo:
>     def __init__(self):
>         self.data = range(10)
>         
>     def __iter__(self):
>         def _my_iter():
>             for e in self.data:
>                 yield e
>         return _my_iter()
> 
> 
> for i in foo():
>     print i
>     
> 
>