[Python-Dev] The iterator story

[Aahz]

On Sat, Jul 20, 2002, Oren Tirosh wrote:
> On Fri, Jul 19, 2002 at 04:22:26PM -0700, Neil Schemenauer wrote:
>> Neal Norwitz wrote:
>>>
>>> In what context?  Were you iterating over a file or something else?
>>> I'm wondering if this is a problem, perhaps pychecker could generate
>>> a warning?
>> 
>> I was switching between implementing something as a generator and
>> returning a list.  I was curious why I was getting different behavior
>> until I realized I was iterating over the result twice.  I don't
>> think pychecker could warn about such a bug.
> 
> That's the scenario that bit me too.  For me it was a little more difficult
> to find because it was wrapped in a few layers of chained transformations.
> I can't tell by the last element in the chain whether the first one is 
> re-iterable or not. 
> 
> My suggestion (which was rejected by Guido) was to raise an error when an
> iterator's .next() method is called afer it raises StopIteration.  This
> way, if I try to iterate over the result again at least I'll get and error
> like "IteratorExhaustedError" instead something that is indistinguishable
> from an iterator of an empty container. I hate silent errors.

I'm still not understanding how this would help.  When a chainable
transformer gets StopIteration, it should immediately return.  What else
do you want to do?
-- 
Aahz (aahz@pythoncraft.com)           <*>         http://www.pythoncraft.com/

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