Python recursion with list returns None [duplicate]

Question

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

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

Ignacio Vazquez-Abrams · Accepted Answer · 2010-04-08 10:44:34Z

20

You don't return anything in the else clause:

    else:
        return foo(a)

answered Apr 8, 2010 at 10:44

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