attribute.py

class Attribute(object):   
    def __get__(self, instance, owner):
        print("Getting x")
        if not 'x' in instance.__dict__:
            instance.__dict__['x']  = 1
        return instance.__dict__['x']

    def __set__(self, instance, value):
        instance.__dict__['x'] = value

class Object(object):
    x = Attribute()

o = Object()

print(o.x)

# Getting x
# 1

o.x = 2

print(o.x)

# Getting x
# 2