python: circular queue

class cirQueue():
    def __init__(self, size):
        self.size = size
        self.array = [None] * self.size
        self.front = -1
        self.rear = -1
        
    def isFull(self):
        if self.front == self.rear + 1 and self.front != -1:
            return True
        return False
    
    def isEmpty(self):
        if self.front == -1:
            return True
        return False
    
    def enQueue(self, element):
        if self.isFull():
            raise Exception("Queue is full")
        if self.front == -1:
            self.front = 0
        if self.rear == self.size - 1:
            self.rear = 0
        else:
            self.rear += 1
        self.array[self.rear] = element
    
    def deQueue(self):
        if self.isEmpty():
            raise Exception("Queue is empty")
        data = self.array[self.front]
        if self.front == self.rear:
            self.front = -1
            self.rear = -1
            self.array = [None for _ in range(self.size)]
        else:
            self.front += 1
        return data

    def display(self):
        print(self.array)