Queue_using_Stacks

class QueueUsingTwoStacks:
    def __init__(self):
        #stack for enqueue operation
        self.stack1=[]
        #stack for dequeue operation
        self.stack2=[]
    def enqueue(self,item):
        #append the items into stack1
        self.stack1.append(item)
    def dequeue(self):
        #check if stack2 is empty or not
        if not self.stack2:
            #if stack2 is empty go to stack1
            while self.stack1:
                #append the pop items of stack1 into stack2
                self.stack2.append(self.stack1.pop())
        if not self.stack2:
            raise IndexError("Dequeue from an empty stack")
        return self.stack2.pop()
queue=QueueUsingTwoStacks()
queue.enqueue(1)
queue.enqueue(2)
print(queue.dequeue())
queue.enqueue(3)
print(queue.dequeue())
print(queue.dequeue())