python 用数组实现队列

# 数组有一个固定的长度。头指针和尾指针，都指向数组第一个值。
# 当进行push操作的时候，头指针后移。当进行pop操作的时候，尾指针向后移
# 当到达最后一个值的时候，重新指向第一个值。取模 %queue_size()



# 首先实现一个数组

class Array(object):
    def __init__(self,size = 32):
        self._size = size
        self._items = [None] * size  # 容器_items, 是一个每个值为None的列表


    def __getitem__(self, index):      # 实现下标访问
        return self._items[index]


    def __setitem__(self, index, value):
        self._items[index] = value


    def __len__(self):
        return self._size


    def clear(self, value=None):
        for i in range(len(self._items)):
            self._items[i] = value


    def __iter__(self):
        for item in self._items:
            yield item



class ArrayQueue(object):
    def __init__(self, maxsize):
        self.maxsize = maxsize
        self.array = Array(maxsize)
        self.head = 0
        self.tail = 0


    def push(self, value):
        if len(self) >= self.maxsize:
            raise Exception('queue full')

        self.array[self.head % self.maxsize] = value
        self.head += 1


    def pop(self):
        value = self.array[self.tail % self.maxsize]
        self.tail += 1
        return value


    def __len__(self):
        return self.head - self.tail









def test_arrrayqueue():

    import pytest
    size = 5
    q = ArrayQueue(size)
    for i in range(size):
        q.push(i)

    assert len(q) == size


    assert q.pop() == 0


    assert q.pop() == 1
    q.push(5)
    assert len(q) == 4
    assert q.pop() == 2
    assert q.pop() == 3
    assert q.pop() == 4
    assert q.pop() == 5

    assert len(q) == 0