Private class data members

Hi

OK, so I am reading on OOP in Python, and I am an old C/C++ programmer so I have somewhat high expectations .

My question is regarding private/public variables. Per default, all class data members are public, but if we precede them with a double underscore, they become private.

1) In the following, why can’t I access *data*? It is private, so it should be available to only class methods, which *output* is:

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class Test():
    __data = 1

    def output(self):
        print Test.data

ins = Test()
ins.output()

class Test():<br /><br /> __data = 1</p><br /><p> def output(self):<br /><br /> print Test.data</p><br /><p>ins = Test()<br /><br />ins.output()

2) The following is OK, i.e. I can’t access the *data* member from outside the class:

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class Test():
    __data = 1

    def output(self):
        print Test.data

ins = Test()
print ins.data

class Test():<br /><br /> __data = 1</p><br /><p> def output(self):<br /><br /> print Test.data</p><br /><p>ins = Test()<br /><br />print ins.data

3) In the following, why can I access the private member *data* from the outside?

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class Test():
    __data = 1

    def output(self):
        print Test.data

Test.data = 2

class Test():<br /><br /> __data = 1</p><br /><p> def output(self):<br /><br /> print Test.data</p><br /><p>Test.data = 2

Any help is appreciated.

Best,

Niles.

http://bit.ly/p64MZq