You can include none at all if the function is being used as a procedure and has no useful return value.

如果函数被用作一个过程，并且没有任何有用的返回值，那么可以不包含return语句。

youdao

Right.? I'm going to set up a variable to say, none what's the answer I want to return, is it there or not. Initially it's got that funny value none.

看我要找的答案在不在数组里面，初始化为,然后建立一个索引。

麻省理工公开课 - 计算机科学及编程导论课程节选

So the question was, why is this return down at this level, it says, well if I ever execute out of this FOR loop, I get to the end of the FOR loop without hitting that branch that took me through the return, then and only then do I want to actually say, gee, I got to this place, there isn't any value to return, none I'm going to return none and none.

问题是，为什么它是在这个级别上返回值呢，意思就是如果我出了这个for循环,就意味着我运行的过程中没有走到任何,带return的支路上去,这时也只有这时我才能说天呐,我终于走到这儿了，这时不会返回任何值，只会返回none和。

麻省理工公开课 - 计算机科学及编程导论课程节选