python实现列表排序sort函数，要求支持任意类型元素的排序，也支持降序

def list_sort(lt, key=None, reverse=True):
    a = len(lt)
    for i in range(a-1):
        for j in range(a-1-i):
            if key:
                if reverse:
                    if key[j]>key[j+1]:
                        key[j],key[j+1] = key[j+1],key[j]
                else:
                    if key[j]<key[j+1]:
                        key[j],key[j+1] = key[j+1],key[j]

            else:
                if reverse:
                    if lt[j]>lt[j+1]:
                        lt[j],lt[j+1] = lt[j+1],lt[j]
                else:
                    if lt[j]<lt[j+1]:
                        lt[j],lt[j+1] = lt[j+1],lt[j]