长度 3 的窗口里最大的和

数组是 [17, 8, 15, 13, 23, 24, 19]，窗口长度 3。运行下面这段程序：

def max_window(a, k):
    s = 0
    for i in range(k):
        s += a[i]
    best = s
    for i in range(k, len(a)):
        s += a[i] - a[i - k]
        if s > best:
            best = s
    return best

print(max_window([17, 8, 15, 13, 23, 24, 19], 3))