class DescState:                           # Use descriptor state
    def __init__(self, value):
        self.value = value

    def __get__(self, instance, owner):    # On attr fetch
        print('DescState get')
        return self.value * 10

    def __set__(self, instance, value):    # On attr assign
        print('DescState set')
        self.value = value

# Client class
class CalcAttrs:
    X = DescState(2)                       # Descriptor class attr
    Y = 3                                  # Class attr
    def __init__(self):
        self.Z = 4                         # Instance attr

obj = CalcAttrs()
print(obj.X, obj.Y, obj.Z)                 # X is computed, others are not
obj.X = 5                                  # X assignment is intercepted
CalcAttrs.Y = 6                            # Y reassigned in class
obj.Z = 7                                  # Z assigned in instance
print(obj.X, obj.Y, obj.Z)

obj2 = CalcAttrs()                         # But X uses shared data, like Y!
print(obj2.X, obj2.Y, obj2.Z)