请按以下描述，自定义数据结构，实现一个circular bufferIn computer science, a circular buffer, circular queue, cyclic buffer or ring buffer is a data structure that uses a single,fixed-size buffer as if it were connected end-to-end. This structure lends itself easily to bufering data streams. There were earlycircular buffer implementations in hardware. A circular buffer first starts out empty and has a set length. In the diagram below is a 7-element buffeiAssume that 1 is written in the center of a circular buffer (the exact starting locatiorimportant in a circular buffer)8Then assume that two more elements are added to the circulal2buffers use FIFOlf two elements are removed, the two oldest values inside of the circulal(first in, first out) logic. n the example, 1 8 2 were the first to enter the cremoved,leaving 3 inside of the buffer.If the buffer has 7 elements, then it is completely full6 7 8 5 3 4 5A property of the circular buffer is that when it is full and a subsequent write is performed,overwriting the oldesdata. In the current example, two more elements - A & B - are added and theythe 3 & 475 Alternatively, the routines that manage the buffer could prevent overwriting the data and retur an error or raise an exceptionWhether or not data is overwritten is up to the semantics of the buffer routines or the application using the circular bufer.Finally, if two elements are now removed then what would be retured is not 3 & 4 but 5 8 6 because A & B overwrote the 3 &the 4 yielding the buffer with: 705A

自定义数据结构CircularBuffer类，实现一个循环缓冲区：

class CircularBuffer:
    def __init__(self, capacity):
        self.buffer = [None] * capacity
        self.capacity = capacity
        self.head = 0
        self.tail = 0
        self.size = 0

    def is_empty(self):
        return self.size == 0

    def is_full(self):
        return self.size == self.capacity

    def enqueue(self, item):
        if self.is_full():
            self.dequeue()

        self.buffer[self.tail] = item
        self.tail = (self.tail + 1) % self.capacity
        self.size += 1

    def dequeue(self):
        if self.is_empty():
            raise Exception("Circular buffer is empty")

        item = self.buffer[self.head]
        self.buffer[self.head] = None
        self.head = (self.head + 1) % self.capacity
        self.size -= 1

        return item

    def peek(self):
        if self.is_empty():
            raise Exception("Circular buffer is empty")

        return self.buffer[self.head]

    def __len__(self):
        return self.size

CircularBuffer类有以下属性和方法：

- `__init__(self, capacity)`: 构造函数，初始化循环缓冲区的容量，头部和尾部指针以及当前元素个数。
- `is_empty(self)`: 判断循环缓冲区是否为空。
- `is_full(self)`: 判断循环缓冲区是否已满。
- `enqueue(self, item)`: 往循环缓冲区中添加元素。
- `dequeue(self)`: 从循环缓冲区中删除最老的元素。
- `peek(self)`: 查看循环缓冲区中最老的元素。
- `__len__(self)`: 得到循环缓冲区中当前元素个数。