Why does my Python inheritance/super example not work?

Question

Why doesn't the following work:

class CTest(tuple):
    def __init__(self,arg):
        if type(arg) is tuple:
            super(CTest,self).__init__((2,2))
        else:
            super(CTest,self).__init__(arg)
a=CTest((1,1))
print a

The ouput is (1,1), while I expect to see (2,2).

Also, why do I get a deprecation warning that object.init() takes no parameters? What should I do instead?

@PetrAbdulin - From the looks of it, Python. – Dominic K Apr 05 '12 at 04:14 — Dominic K, Apr 05 '12 at 04:14
Corrected, sorry. It is Python. – user1308523 Apr 05 '12 at 04:14 — user1308523, Apr 05 '12 at 04:14

score 5 · Accepted Answer · edited May 23 '17 at 10:34

5

Tuples are immutable, you have to override __new__:

class CTest(tuple):
    def __new__(cls, arg):
        if type(arg) is tuple:
            return super(CTest, cls).__new__(cls, (2, 2))
        else:
            return super(CTest, cls).__new__(cls, arg)

Now this works as expected:

a = CTest((1,1))
print a
> (2, 2)

Take a look at this post for further details.

edited May 23 '17 at 10:34

Community

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answered Apr 05 '12 at 04:16

Óscar López

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Why does my Python inheritance/super example not work?

1 Answers1