[Python-Dev] bool(iter([])) changed between 2.3 and 2.4

Guido van Rossum guido at python.org
Wed Sep 21 02:11:35 CEST 2005

On 9/20/05, Terry Reedy <tjreedy at udel.edu> wrote:
> I presume there were two reasons: internal efficiency of preallocations
> (list(some_it) for example)

This could have been implemented without making the implementation
details public.

> and letting people differentiate iterator with
> something left to return versus nothing, just as we can differentiate
> collections with something versus nothing.

But this is against the very idea of the iterator protocol -- for
general iterators, there may be no way to determine whether there is a
next item without actually producing the item, so the proper approach
is to code with that in mind. When this type of look-ahead is
required, a buffering iterator should be inserted, so that the
algorithm can work with all iterators rather than only with iterators
over built-in containers.

--Guido van Rossum (home page: http://www.python.org/~guido/)

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