[Python-Dev] Single- vs. Multi-pass iterability

[Greg Ewing]

> Imagine an altenative universe where a south african programmer called
> Rossu van Guidom writes a wonderful language called Mamba and in that
> language iterator semantics are defined like this:
> 
> * Objects that wish to be iterable define an __iter__() method returning an
> iterator.
> 
> * An iterator is an object with a next() method. That's all.

But that doesn't allow for things like file objects, which,
although not iterators themselves, are capable of producing
iterators of different sorts which iterate over them in
different ways -- and yet they can only be iterated over
once.

In other words, there are such things as one-shot
iterables, even if iterables and iterators are kept
separate.

Maybe a one-shot iterable should raise an exception
if you try to obtain a second iterator from it?

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
Christchurch, New Zealand	   | wholly-owned subsidiary of USA Inc.  |
greg@cosc.canterbury.ac.nz	   +--------------------------------------+