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pythoninheritancesubclasspython-2.5

Subclassing int in Python

I'm interested in subclassing the built-in int type in Python (I'm using v. 2.5), but having some trouble getting the initialization working.

Here's some example code, which should be fairly obvious.

class TestClass(int):
    def __init__(self):
        int.__init__(self, 5)

However, when I try to use this I get:

>>> a = TestClass()
>>> a
0

where I'd expect the result to be 5.

What am I doing wrong? Google, so far, hasn't been very helpful, but I'm not really sure what I should be searching for

Solution

  • int is immutable so you can't modify it after it is created, use __new__ instead

    class TestClass(int):
    def __new__(cls, *args, **kwargs):
        return  super(TestClass, cls).__new__(cls, 5)

print TestClass()