Why is there no __iter__() for lists strings and tuples?

[Oren Tirosh]

On Sat, Dec 21, 2002 at 11:43:31PM -0300, Walter Moreira wrote:
> Sometime ago I also thought that this was the equivalence with the 'for'
> loop.  But if you do:
> 
>     >>> for i in [1,2,3]:
>     ...     raise StopIteration
>     ...
>     Traceback (most recent call last):
>       File "<stdin>", line 2, in ?
>     StopIteration
>     >>>
> 
> So, it is not completely equivalent. I expected the StopIteration to
> finalize the 'for' loop.  On the other hand, if the exception is raised
> from the iterator, the loop ends.  Why does this asymmetric behavior
> ocurr?

Internally, the tp_next slot does not actually use the StopIteration
exception.  It just returns NULL (for performance). A real exception is
only used when tp_next is exposed to Python code as the .next() method.

	Oren