带列表的Python递归返回None [英] Python recursion with list returns None

问题描述

def foo(a):
    a.append(1)
    if len(a) > 10:
        print a
        return a
    else:
        foo(a)

为什么此递归函数返回None(请参阅下面的记录)?我不太明白自己在做什么错.

Why this recursive function returns None (see transcript below)? I can't quite understand what I am doing wrong.

In [263]: x = []

In [264]: y = foo(x)
[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

In [265]: print y
None

推荐答案

您不会在else子句中返回任何内容:

You don't return anything in the else clause:

    else:
        return foo(a)

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