编写程序实现循环队列的初始化，判断队列是否为空，入队列和出队列

循环队列是一种特殊的队列，它可以在一定程度上避免队列的溢出问题。下面是实现循环队列的基本操作：

1.初始化队列：

class CircularQueue:
    def __init__(self, capacity):
        self.capacity = capacity
        self.queue = [None] * capacity
        self.head = -1
        self.tail = -1

2.判断队列是否为空：

    def is_empty(self):
        return self.head == -1

3.入队列：

    def enqueue(self, item):
        if (self.tail + 1) % self.capacity == self.head:
            print("Queue is full.")
            return
        elif self.is_empty():
            self.head = 0
            self.tail = 0
            self.queue[self.tail] = item
        else:
            self.tail = (self.tail + 1) % self.capacity
            self.queue[self.tail] = item

4.出队列：

    def dequeue(self):
        if self.is_empty():
            print("Queue is empty.")
            return None
        elif self.head == self.tail:
            item = self.queue[self.head]
            self.head = -1
            self.tail = -1
            return item
        else:
            item = self.queue[self.head]
            self.head = (self.head + 1) % self.capacity
            return item

完整代码如下：

class CircularQueue:
    def __init__(self, capacity):
        self.capacity = capacity
        self.queue = [None] * capacity
        self.head = -1
        self.tail = -1
        
    def is_empty(self):
        return self.head == -1
        
    def enqueue(self, item):
        if (self.tail + 1) % self.capacity == self.head:
            print("Queue is full.")
            return
        elif self.is_empty():
            self.head = 0
            self.tail = 0
            self.queue[self.tail] = item
        else:
            self.tail = (self.tail + 1) % self.capacity
            self.queue[self.tail] = item
            
    def dequeue(self):
        if self.is_empty():
            print("Queue is empty.")
            return None
        elif self.head == self.tail:
            item = self.queue[self.head]
            self.head = -1
            self.tail = -1
            return item
        else:
            item = self.queue[self.head]
            self.head = (self.head + 1) % self.capacity
            return item

使用示例：

q = CircularQueue(5)
print(q.is_empty())  # True
q.enqueue(1)
q.enqueue(2)
q.enqueue(3)
q.enqueue(4)
q.enqueue(5)
q.enqueue(6)  # "Queue is full."
print(q.dequeue())  # 1
print(q.dequeue())  # 2
q.enqueue(6)
q.enqueue(7)  # "Queue is full."
print(q.dequeue())  # 3
print(q.dequeue())  # 4
print(q.dequeue())  # 5
print(q.dequeue())  # 6
print(q.is_empty())  # True