sort与sorted讲解，以及 list_b = list_a.sort()中 list_b为什么输出为none

https://blog.youkuaiyun.com/weixin_43790276/article/details/90247230?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522160457804619724836741639%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fall.%2522%257D&request_id=160457804619724836741639&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2_allfirst_rank_v2~rank_v28-1-90247230.first_rank_ecpm_v3_pc_rank_v2&utm_term=a%3Db.sort%E4%B8%BA%E4%BB%80%E4%B9%88%E6%98%AF%E9%94%99%E7%9A%84python&spm=1018.2118.3001.4449