Python for 循环迭代未完成，跳过步骤

Question

I got a 'wrong answer' error in my " queue from stack " algorithm when I expected it to work. For those not familiar with the algorithm, the solution requires two stacks of list type- a "push stack" and a 'pop stack', which is in effect a queue buffer that the push stack dumps itself into when the queue stack gets called and is empty. See if you can determine what's going on and where the problem is.

def pop(self):
    self.stack_to_push_to= [1,2] # sample hard coding
    self.queue_to_pop = [] # sample hard coding

    if self.queue_to_pop == 0: # trigger a dump to form a new queue buffer
        for _ in stack_to_push_to:
            self.queue_to_pop.append(self.stack_to_push_to.pop())
    print(self.queue_to_pop) # [2] but expected [2,1]

Answer 1

Too much was being done on the append line, clever and concise though it seemed to be. When one pops from an iterable that is currently being iterated on, it confuses the count and python iterator process, or that's what I'm guessing is happening. A similar thing happens in excel when you delete rows while at the same time traversing down them (not up them though). I just assumed Python would have been able to handle this on it's own somehow.

Problematic code.

if self.queue_to_pop == 0: # trigger a dump to form a new sub-queue
    for _ in stack_to_push_to:
        self.queue_to_pop.append(self.stack_incoming.pop()) #!!!!!!

The pop method served the interest of automatically working backwards, which I want, and I also thought it would save time and space complexity, but it ultimately didn't work and I found two alternatives that do. I'd be interested in learning if there's a way to reduce the complexities of my solutions.

Option 1:

    for i in range(len(self.stack_to_push_to)-1,-1,-1):
        self.queue_buffer.append(self.stack_to_push_to[i])
    self.stack_to_push_to = []

Option 2:

    for _ in reversed(self.stack_to_push_to):
        self.queue_buffer.append(_)
    self.stack_to_push_to = []

I didn't see anyone else post this issue so I thought it was worth sharing and hope it enlightens others.