QueuesDataStructure.py

# Implementation of the FIFO Property using Python Queues
# Class definition
class QueueData:
    # An empty queue that will store the elements
    def __init__(self):
        self.data = []
            
    # enqueue() method
    # Adding the first element e to the queue
    def enqueue(self, e):
        self.data.insert(0, e)
    
    # dequeue() method
    # Removing and returning the element from the front (FIFO)
    # Raise an exception if the queue is empty
    def dequeue(self):
        if self.is_empty():
            raise IndexError("Queue is empty")
        else:
            return self.data.pop()
    
    # peek() method
    # Returning the first element of the queue
    # Raise exception if the queue is empty
    def peek(self):
        if self.is_empty():
            raise IndexError("Queue is Empty")
        else:
            return self.data[-1]

    # size() method
    # Returning True if the Queue is Empty
    def is_empty(self):
        return len(self.data) == 0
    # Returning the number of elements in the Queue
    def size(self):
        return len(self.data)

# Object Instantiation and Queue Implementations
Q = QueueData()
Q.enqueue("M")             # M
Q.enqueue("O")             # O
Q.enqueue("N")             # N
Q.enqueue("D")             # D
Q.enqueue("A")             # A
Q.enqueue("Y")             # Y
print(Q.peek())
print(Q.size())
print(Q.is_empty())
print(Q.dequeue())       # M
print(Q.dequeue())       # O
print(Q.dequeue())       # N
print(Q.dequeue())       # D
print(Q.dequeue())       # A
print(Q.dequeue())       # Y
print(Q.is_empty())      # True
print(Q.size())          # 0
print(Q.peek())          # IndexError: Queue is Empty