In [3]:
class Queue:
    def __init__(self):
        self.items = []
        
    def is_empty(self):
        return self.items == []
    
    def enqueue(self, item):
        self.items.insert(0, item) # this insert is actually a O(n)
        
    def dequeue(self):
        return self.items.pop()
    
    def size(self):
        return len(self.items)