python希尔排序算法是什么？

def shellSort(arr):

    import math

    gap=1

    while(gap < len(arr)/3):

        gap = gap*3+1

    while gap > 0:

        for i in range(gap,len(arr)):

            temp = arr[i]

            j = i-gap

            while j >=0 and arr[j] > temp:

                arr[j+gap]=arr[j]

                j-=gap

            arr[j+gap] = temp

        gap = math.floor(gap/3)

    return arr

}