[Python-Dev] PEP 246: lossless and stateless (original) (raw)

Alex Martelli aleax at aleax.it
Sun Jan 16 09:23:26 CET 2005

On 2005 Jan 16, at 03:17, Phillip J. Eby wrote: ...

Uh oh. I just used "view" to describe an iterator as a view on an iterable, as distinct from an adapter that adapts a sequence so that it's iterable. :)

I.e., using "view" in the MVC sense where a given Model might have multiple independent Views.

I think that in order to do that you need to draw a distinction between two categories of iterables: so, again, a problem of terminology, but one connected to a conceptual difference.

An iterator IS-AN iterable: it has iter. However, it can't have "multiple independent views"... except maybe if you use itertools.tee for that purpose.

Other iterables are, well, ``re-iterables'': each call to their iter makes a new fresh iterator, and using that iterator won't alter the iterable's state. In this case, viewing multiple iterators on the same re-iterables as akin to views on a model seems quite OK.

I can't think of any 3rd case -- an iterable that's not an iterator (iter does not return self) but neither is it seamlessly re-iterable. Perhaps the ``file'' built-in type as it was in 2.2 suffered that problem, but it was a design problem, and is now fixed.

Alex

More information about the Python-Dev mailing list