In [46]:

    

class Stack:
    def __init__(self):
        self.items = []
    
    def __str__(self):
        string = ""
        if len(self.items) != 0:
            for i in xrange(len(self.items)-1, -1, -1):
                string += "{0}\n".format(self.items[i])
        return string
    
    def pop(self):
        if self.items != []:
            return self.items.pop()
        else:
            return None
    
    def push(self, item):
        self.items.insert(0, item)
    
    def peek(self):
        return self.items[-1]


    

In [47]:

    

stack = Stack()
print(stack)
stack.push(1)
print(stack)
stack.push(2)
print(stack)
stack.push(3)
print(stack)
print("Peeking at {0}".format(stack.peek()))
print("Popped off {0}".format(stack.pop()))
print(stack)


    

    




1

1
2

1
2
3

Peeking at 1
Popped off 1
2
3

In [55]:

    

class Queue:
    def __init__(self):
        self.items = []
        
    def __str__(self):
        string = ""
        for item in self.items:
            string += "{0}\n".format(item)
        return string
    
    def enqueue(self, item):
        self.items.append(item)
    
    def dequeue(self):
        if self.items != []:
            return self.items.pop(0)
        else:
            return None


    

In [56]:

    

queue = Queue()
print(queue)
queue.enqueue(1)
print(queue)
queue.enqueue(2)
print(queue)
queue.enqueue(3)
print(queue)
queue.dequeue()
print(queue)


    

    




1

1
2

1
2
3

2
3

In [49]: