Conditionally implementing __iter__ in new style classes

[Leif K-Brooks]

Thomas Heller wrote:
> I forgot to mention this: The Base class also implements a __getitem__
> method which should be used for iteration if the .Iterator method in the
> subclass is not available.  So it seems impossible to raise an exception
> in the __iter__ method if .Iterator is not found - __iter__ MUST return
> an iterator if present.

def Iterator(self):
    for index in xrange(len(self)):
        yield self[index]

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

...and then override Iterator in subclasses. But this raises the
question of why you need to use a specially-named method instead of
having subclasses override the __iter__.