函数返回无 [英] Function returns None

问题描述

在犯错误然后进行递归后，我得到了 None.

After making an error then doing recursion i get None.

def getplayerinput():
    a = ["rock","paper","scissors"]
    plin = raw_input("Choose %s/%s/%s: " %(a[0], a[1], a[2]))
    print plin,'-first print'
    if plin not in a:
        print "Wrong input"
        getplayerinput()
    else:
        print plin,'-second print'
        return plin

for i in range(0,11):
    print getplayerinput()

如果您先输入rock"，然后输入cat"，然后输入paper"，您将得到None".

If you input first 'rock' then 'cat' then 'paper' you will get a 'None'.

推荐答案

一旦输入无效，您就不会返回任何内容.改为这样做:

You do not return anything once the input is not valid. Do this instead:

def getplayerinput():
    a = ["rock","paper","scissors"]
    plin = raw_input("Choose %s/%s/%s: " %(a[0], a[1], a[2]))
    print plin,'-first print'
    if plin not in a:
        print "Wrong input"
        return getplayerinput() # <- added return
    else:
        print plin,'-second print'
        return plin

for i in range(0,11):
    print getplayerinput()

否则递归调用会向顶级调用返回一些东西，但它只会吞下递归调用的返回值，因为它不会通过 return 传递它.

Otherwise the recursion call will return something to a top level call, but that one just swallows the return value from the recursion call, since it doesn't pass it on via return.

这篇关于函数返回无的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！