On Jan 15, 2005, at 6:02 PM, Simon Percivall wrote:
On 2005-01-15, at 23.50, Just van Rossum wrote:Phillip J. Eby wrote:
But it _does_ perform an implicit adaptation, via PyObject_GetIter.
First, that's not implicit. Second, it's not adaptation, either. PyObject_GetIter invokes the '__iter__' method of its target -- a method that is part of the *iterable* interface. It has to have something that's *already* iterable; it can't "adapt" a non-iterable into an iterable.
Further, if calling a method of an interface that you already have in order to get another object that you don't is adaptation, then what *isn't* adaptation? Is it adaptation when you call 'next()' on an iterator? Are you then "adapting" the iterator to its next yielded value?
That's one (contrived) way of looking at it. Another is that
y = iter(x)
adapts the iterable protocol to the iterator protocol.
Especially since an iterable can also be an object without an __iter__ method but with a __getitem__ method. Calling __iter__ might get an iterator, but calling __getitem__ does not. That seems like adaptation. No? It's still not clear to me, as this shows, exactly what counts as what in this game.
I think that's wrong. To spell iter() in an adapter/interface world, I'd spell iter(obj) as:
adapt(obj, IIterable).iterator()
Then, list, tuple, dict objects would specify that they implement IIterable. There is a default adapter from object->IIterable which provides a .iterate() method which creates an iterator that uses __getitem__ on the adaptee.
In my opinion, adapters provide a different view of an object. I can see treating list "as a" iterable, but not "as a" iterator.
James
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