Circular Queue Implementation in Python

In this source code example, we will write a code to implement the Circular Queue data structure in Python.

A circular queue is the extended version of a regular queue where the last element is connected to the first element. Thus forming a circle-like structure.

The circular queue solves the major limitation of the normal queue. In a normal queue, after a bit of insertion and deletion, there will be non-usable empty space.

Circular Queue Implementation in Python


class CircularQueue(object):
    def __init__(self, limit = 10):
        self.limit = limit
        self.queue = [None for i in range(limit)]  
        self.front = self.rear = -1

    # for printing the queue
    def __str__(self):
        if (self.rear >= self.front):
            return ' '.join([str(self.queue[i]) for i in range(self.front, self.rear + 1)])
  
        else: 
            q1 = ' '.join([str(self.queue[i]) for i in range(self.front, self.limit)])
            q2 = ' '.join([str(self.queue[i]) for i in range(0, self.rear + 1)])
            return q1 + ' ' + q2

    # for checking if queue is empty
    def isEmpty(self):
        return self.front == -1

    # for checking if the queue is full
    def isFull(self):
        return (self.rear + 1) % self.limit == self.front

    # for adding an element to the queue
    def enqueue(self, data):
        if self.isFull():
            print('Queue is Full!')
        elif self.isEmpty():
            self.front = 0
            self.rear = 0
            self.queue[self.rear] = data
        else:
            self.rear = (self.rear + 1) % self.limit  
            self.queue[self.rear] = data 

    # for removing an element from the queue
    def dequeue(self):
        if self.isEmpty():
            print('Queue is Empty!')
        elif (self.front == self.rear):  
            self.front = -1
            self.rear = -1
        else:
            self.front = (self.front + 1) % self.limit 

if __name__ == '__main__':
    myCQ = CircularQueue(5)
    myCQ.enqueue(14)
    myCQ.enqueue(22)
    myCQ.enqueue(13)
    myCQ.enqueue(16)
    print('Queue:',myCQ)
    myCQ.dequeue()
    myCQ.dequeue()
    print('Queue:',myCQ)
    myCQ.enqueue(9)
    myCQ.enqueue(20)
    myCQ.enqueue(5)
    myCQ.enqueue(5)
    print('Queue:',myCQ)

Output:

Queue: 14 22 13 16
Queue: 13 16
Queue is Full!
Queue: 13 16 9 20 5

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