Newbie Q: Class Privacy (or lack of)

[Timo]

Steve Jobless kirjoitti:

> Let's say the class is defined as:
>
>   class MyClass:
>     def __init__(self):
>       pass
>     def func(self):
>       return 123
>
> But from the outside of the class my interpreter let me do:
>
>   x = MyClass()
>   x.instance_var_not_defined_in_the_class = 456
>
> or even:
>
>   x.func = 789
>
> After "x.func = 789", the function is totally shot.
>

You can avoid the problem by using the __slots__ definition and
new-style classes (inherit from object):

class MyClass(object):

    __slots__ = ('bar',)

    def func(self):
        return 123

x = MyClass()
x.instance_var_not_defined_in_the_class = 456
==>
AttributeError: 'MyClass' object has no attribute
'instance_var_not_defined_in_the_class'

x.func = 789
==>
AttributeError: 'MyClass' object attribute 'func' is read-only

Only the bar-attribute can be set:

x.bar = 'foo'

-- timo