python两个栈实现一个队列

class Stsck:
    def __init__(self):
        self.queue1 = []
        self.queue2 = []

    def push(self, elem):
        self.queue1.append(elem)

    def pop(self):
        if len(self.queue1) == 0:
            return None
        while len(self.queue1) != 1:
            self.queue2.append(self.queue1.pop(0))
        self.queue1, self.queue2 = self.queue2, self.queue1
        return self.queue2.pop()


st = Stsck()
if __name__ == "__main__":
    for i in range(5):
        st.push(i)

    for i in range(3):
        print(st.pop())

    for i in range(5, 10):
        st.push(i)

    for i in range(7):
        print(st.pop())