[Python-Dev] The purpose of SETUP_LOOP, BREAK_LOOP, CONTINUE_LOOP

[P.J. Eby]

At 08:25 AM 3/12/2011 -0500, Eugene Toder wrote:
>Right, I'm not suggesting to remove all blocks, only SETUP_LOOP
>blocks. Do you see the problem in that case?

I think you guys are forgetting about FOR_ITER, listcomps, and the like.

That is, IIRC, the reason loops use the block stack is because they 
put things on the regular stack, that need to be cleared off the 
stack when the loop is exited (whether normally or via an exception).

In other words, just jumping out of a loop without popping the block 
stack would leave junk on the regular stack, thereby failing to 
deallocate the loop iterator.  In the case of a nested loop, this 
would also mean that the outer loop would start using the inner 
loop's iterator, and all sorts of hilarity would then ensue.