InClassQueue.py

class Stack(object):

    def __init__(self):
        self.stack = []

    # add an item to the top of the stack
    def push(self, item):
        self.stack.append(item)

    # remove an item from the top of the stack
    def pop(self):
        if not self.isEmpty():
            return self.stack.pop()
        else:
            return None

    # check what item is on top of the stack without removing it
    def peek(self):
        return self.stack[len(self.stack) - 1]

    # check if a stack is empty
    def isEmpty(self):
        return len(self.stack) == 0

    # return the number of elements in the stack
    def size(self):
        return len(self.stack)

    # a string representation of this stack.
    def __str__(self):
        return str(self.stack)


class NewQueue(object):
    def __init__(self):
        self.stack1 = Stack()
        self.stack2 = Stack()

    # O(1) complexity since execution occurs in place
    def enqueue(self, item):
        self.stack1.push(item)

    # O(n) time complexity since n pushes and pops occur due to the while loop
    def dequeue(self):
        if not self.stack2.isEmpty():
            while not self.stack1.isEmpty():
                self.stack2.push(self.stack1.pop())
        return self.stack2.pop()

    def isEmpty(self):
        return len(self.stack1) == 0

    def size(self):
        return len(self.stack1)

    # a string representation of this stack.
    def __str__(self):
        return str(self.stack1)