[Python-Dev] PEP 3142: Add a "while" clause to generator expressions

[Alexey G. Shpagin]

On Tue, Jan 20, 2009 at 10:45:27AM -0500, Gerald Britton wrote:
> OK, so your suggestion:
> 
>  g = (n for n in range(100) if n*n < 50 or raiseStopIteration())
> 
> really means "return in in the range 0-99 if n-squared is less than 50
> or the function raiseStopIteration() returns True".
> 
> How would this get the generator to stop once n*n >=50? It looks
> instead like the first time around, StopIteration will be raised and
> (presumably) the generator will terminate.

Just test it. After the generator is terminated, no one will call
 range(100).next()
method, if I really understand you.

Maybe (as suggested before with 'if ... else break`) we should rename
function raiseStopIteration() to else_break(),
since it looks to me being a 'if ... else break's implementation with functions.

Example will look like
 g = (n for n in range(100) if n*n < 50 or else_break())

That's to the matter of taste, I think.

--
Alexey G. Shpagin