将 random.choice 的结果添加到类中的空列表的问题

Question

我无法理解我为学校作业编写的以下代码的输出。

class Number:

  def __init__(self):

    self.__number = []

 

  def pick_num(self, my_list):

    x = random.choice(my_list)

    self.__number = self.__number.append(x)
  
    return print("Here's your list with the added number: ", self.__number)

def main()

    random_number = Number()

    my_list = [1, 2, 3, 4]

    random_number.pick_num(my_list)

main()

输出

Here's your list with the added number: None

我不明白为什么我得到 None 而不是想要的输出 [n]

Answer 1

import random

class Number:

    def __init__(self):
        self.__number = []

    def pick_num(self, my_list):
        x = random.choice(my_list)

        self.__number.append(x)

        return print("Here's your list with the added number: ", self.__number)


def main():

    random_number = Number()

    my_list = [1, 2, 3, 4]

    random_number.pick_num(my_list)


main()

.append 返回 None 并修改它调用的列表。