py-private-attributes.ipynb

Kernel: Python 3 (system-wide)

How/Why private attribtues in python classes?

Scenario 1

We have a parent/child inheritance, which uses the same variable names.

class Foo1(object):
    def __init__(self, x):
        self.x = x
    def get_x(self):
        return self.x

class Bar1(Foo1):
    def __init__(self, x):
        super().__init__(x)
        self.x = 2*x
    def parent_x(self):
        return super().get_x()

a1 = Foo1(123)
a1.get_x()

123

Note, the get_x method comes from the parent class – while the value x from the child class.

b1 = Bar1(123)
b1.get_x()

246

Here is the catch: there is only one x in play and therefore the child class overwrote the parent classes' x attribute.

b1.parent_x()

246

Scenario 2

We use Python's name-mangling (two leading underscores are replaced by _[class name]_) to introduce two x attributes in total. Therefore, we avoid them being overwritten.

class Foo2(object):
    def __init__(self, x):
        self.__x = x
    def get_x(self):
        return self.__x

class Bar2(Foo2):
    def __init__(self, x):
        super().__init__(x)
        self.__x = 2*x
    def get_x(self):
        return self.__x
    def parent_x(self):
        return super().get_x()

a2 = Foo2(123)
a2.get_x()

123

b2 = Bar2(123)
b2.get_x()

246

b2.parent_x()

123