# Python Program to Implement Queues using Stacks class Queue:    def __init__(self):        self.inbox = Stack()        self.outbox = Stack()     def is_empty(self):        return (self.inbox.is_empty() and self.outbox.is_empty())     def enqueue(self, data):        self.inbox.push(data)     def dequeue(self):        if self.outbox.is_empty():            while not self.inbox.is_empty():                popped = self.inbox.pop()                self.outbox.push(popped)        return self.outbox.pop()  class Stack:    def __init__(self):        self.items = []     def is_empty(self):        return self.items == []     def push(self, data):        self.items.append(data)     def pop(self):        return self.items.pop()  a_queue = Queue()while True:    print('enqueue <value>')    print('dequeue')    print('quit')    do = input('What would you like to do? ').split()     operation = do[0].strip().lower()    if operation == 'enqueue':        a_queue.enqueue(int(do[1]))    elif operation == 'dequeue':        if a_queue.is_empty():            print('Queue is empty.')        else:            dequeued = a_queue.dequeue()            print('Dequeued element: ', int(dequeued))    elif operation == 'quit':        break