empty lists vs empty generators

[Terry Reedy]

"Brian Roberts" <brian at mirror.org> wrote in message 
news:509534af.0505021514.5e49aa2 at posting.google.com...
> I'm using using generators and iterators more and more intead of
> passing lists around, and prefer them.  However, I'm not clear on the
> best way to detect an empty generator (one that will return no items)
> when some sort of special case handling is required.

If you write an iterator class instead of the abbreviated generator form, 
and you can tell from the initialization parameters whether there will be 
any data, then you can give the class a __nonzero__ method.  You can also 
have an initially nonempty iterator flag when it becomes empty.

My point is that writing an iterator as a generator is a convenience, not a 
necessity, and that one gives up the full flexibility of an iterator class 
when one does so, but that one is not required to do so.

I quite understanding wanting to have your cake and eat it too.  The 
convenience is sometimes major.

Terry J. Reedy