for what are for/while else clauses

[JCM]

John Roth <newsgroups at jhrothjr.com> wrote:
...
>> >> What are the three conditions?  I know of two:
>> >>
>> >>   1 Reaching the end of the iteration
>> >>   2 Breaking out
>> >      3. Not executing at all.
>>
>> I see that as an example of #1.

> But it isn't. See what your code looks like with an
> empty file, for example. Or even worse, see what it
> would look like if you have to use a generator where
> you can't test for an empty sequence.

Iterating over an empty file behaves as I expect--the loop terminates
after zero iterations, one time for each line.  I'm not sure what you
mean about generators...  If you have a generator that never yields
anything:

  def g():
     if 0:
        yield 'nothing'

(is there a better way of writing one?)
then the loop

  for x in g():
     print x

also terminates after zero iterations.