I think you're on to something. But I think both your examples have a problem, even though your second one "works".

If we weren't forced by backward compatibility I would have made it much harder for StopIteration to "leak out". Currently a generator can either return or raise StopIteration to signal it is done, but I think it would have been better if StopIteration was treated as some kind of error in this case. Basically I think any time a StopIteration isn't caught by a for-loop or an explicit try/except StopIteraton, I feel there is a bug in the program, or at least it is hard to debug.

I'm afraid that ship has sailed, though...

On Sat, Nov 1, 2014 at 7:56 AM, yotam vaknin <tomirendo@gmail.com> wrote:

Hi,

I would like to purpose that generator expressions will not catch StopIteration exception, if this exception did not come from the iterated object's __next__ function specifically. So generator expressions will be able to raise StopIteration by calculating the current value of the Generator.

Here is an example of a use-case :

def izip(*args):
iters = [iter(obj) for obj in args]
while True:
yield tuple(next(it) for it in iters)

a = izip([1,2],[3,4])
print(next(a),next(a),next(a)) #Currently prints : (1, 3) (2, 4) ()
list(izip([1,2],[3,4])) #Currently never returns

Even thought this is the PEP described behaviour, I think this is an unwanted behaviour.

I think Generator Expressions should work like List Comprehension in that sense:

def iizip(*args):
iters = [iter(obj) for obj in args]
while True:
yield tuple([next(it) for it in iters])

tuple(iizip([1,2],[3,4])) #Returns [(1, 3), (2, 4)]

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