[Python-ideas] sentinel_exception argument to `iter`

Hi, This time I'm posting on the right list :) Sorry for the mistake in the last thread. `iter` has a very cool `sentinel` argument. I suggest an additional argument `sentinel_exception`; when it's supplied, instead of waiting for a sentinel value, we wait for a sentinel exception to be raised, and then the iteration is finished. This'll be useful to construct things like this: my_iterator = iter(my_deque.popleft, IndexError) What do you think? Ram.