Iteratoration question

grocery_stocker cdalten at gmail.com
Fri Apr 3 04:19:07 CEST 2009


On Apr 2, 6:33 pm, "Rhodri James" <rho... at wildebst.demon.co.uk> wrote:
> On Fri, 03 Apr 2009 02:07:38 +0100, grocery_stocker <cdal... at gmail.com>
> wrote:
>
> > Okay, I was thinking more about this. I think this is also what is
> > irking me. Say I have the following..
>
> >>>> a = [1,2,3,4]
> >>>> for x in a:
> > ...     print x
> > ...
> > 1
> > 2
> > 3
> > 4
>
> > Would 'a' somehow call __iter__ and next()? If so, does python just
> > perform this magically?
>
> No.  It's "for" that invokes the iteration protocol; that's pretty
> much the definition of it.  You have read the iteration protocol
> after it's been mentioned so many times now, haven't you?
>
> "for" calls iter(a), which in turn calls a.__iter__(), to get an
> iterator.  Once it's got, "for" calls next() on the iterator each
> time round the loop.  Very approximately, that little for-loop
> translates to:
>
> a = [1,2,3,4]
> i = iter(a)
> try:
>      while True:
>          x = i.next()
>         print x
> except StopIteration:
>      pass
>

Okay, at the risk of sounding like a total slacker, I've only briefly
scanned over the iteration protocol. After I get up in the morning,
I'll probably read it more closely.




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