Iterator / Iteratable confusion

[Terry Reedy]

"Francis Girard" <francis.girard at free.fr> wrote in message 
news:200502131958.27410.francis.girard at free.fr...
> An ""iteratable"" class is a class supporting the __iter__ method which 
> should
> return an ""iterator"" instance, that is, an instance of a class 
> supporting
> the "next" method.

Not quite right, see below.

> An iteratable, strictly speaking, doesn't have to support the "next" 
> method

An iterable with a next method is, usually, an iterator.

> an "iterator" doesn't have to support the "__iter__" method

Yes it does.  iter(iterator) is iterator is part of the iterater protocol 
for the very reason you noticed...

>(but this breaks the iteration protocol as we will later see).

Iterators are a subgroup of iterables.  Being able to say iter(it) without 
having to worry about whether 'it' is just an iterable or already an 
iterator is one of the nice features of the new iteration design.

Terry J. Reedy