Advanced Patterns

class A:
    def greet(self):
        return "A"

class B(A):
    def greet(self):
        return "B->" + super().greet()

class C(A):
    def greet(self):
        return "C->" + super().greet()

class D(B, C):
    def greet(self):
        return "D->" + super().greet()

print(D().greet())

class Meta(type):
    def __new__(mcs, name, bases, namespace):
        namespace['created_by'] = 'Meta'
        return super().__new__(mcs, name, bases, namespace)

class MyClass(metaclass=Meta):
    pass

print(MyClass.created_by)
print(type(MyClass))
print(type(Meta))

class Celsius:
    def __init__(self, value=0):
        self._value = value

    def __get__(self, instance, owner):
        return self._value

    def __set__(self, instance, value):
        if value < -273.15:
            raise ValueError("Below absolute zero")
        self._value = value

class Weather:
    temperature = Celsius()

w1 = Weather()
w2 = Weather()
w1.temperature = 25
w2.temperature = 30
print(w1.temperature)