Python: list indices must be integers or slices, not float问题

今天尝试使用PyCharm来编写一个Python程序，结果报错

TypeError: list indices must be integers or slices, not float

出错代码

def quicksort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) / 2] #报错 line4
    left = [x for x in arr if x < pivot]
    middle = [x for x in arr if x == pivot]
    right = [x for x in arr if x > pivot]
    return quicksort(left) + middle + quicksort(right)


print (quicksort([3, 6, 8, 10, 12, 13, 1, 2]))

这是一个简易的快排程序
经过查阅得到 “/”是浮点数除法，但是在此程序中需要整除，所以要用“%”或者“//”

所以经过更改后的Python代码

def quicksort(arr):
    if len(arr) <= 1:
        return arr
    pivot = arr[len(arr) % 2]
    left = [x for x in arr if x < pivot]
    middle = [x for x in arr if x == pivot]
    right = [x for x in arr if x > pivot]
    return quicksort(left) + middle + quicksort(right)


print (quicksort([3, 6, 8, 10, 12, 13, 1, 2]))

结果

[1, 2, 3, 6, 8, 10, 12, 13]

Process finished with exit code 0

成功输出