python中set怎样去重

my_list = [1, 2, 3, 2, 1, 4, 5, 4]
my_set = set(my_list)
new_list = list(my_set)
print(new_list)

[1, 2, 3, 4, 5]

my_list = [1, 2, 3, 2, 1, 4, 5, 4]
new_list = []
for item in my_list:
    if item not in new_list:
        new_list.append(item)
print(new_list)

[1, 2, 3, 4, 5]