class Animal:
    def __init__(self, name):
        self.name = name
    def speak(self):
        return "..."
    def describe(self):
        return f"{self.name} says {self.speak()}"

class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)           # let the parent set up its part
        self.breed = breed
    def speak(self):                     # override
        return "Woof"

d = Dog("Rex", "lab")
print(d.describe())                              # Rex says Woof
print(isinstance(d, Animal), issubclass(Dog, Animal))   # True True

class A:
    def hello(self): return "A"
class B(A):
    def hello(self): return "B→" + super().hello()
class C(A):
    def hello(self): return "C→" + super().hello()
class D(B, C):
    def hello(self): return "D→" + super().hello()

print(D().hello())                          # D→B→C→A
print([k.__name__ for k in D.__mro__])      # ['D', 'B', 'C', 'A', 'object']

from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self) -> float: ...

class Square(Shape):
    def __init__(self, side):
        self.side = side
    def area(self):
        return self.side ** 2

print(Square(3).area())          # 9
try:
    Shape()
except TypeError:
    print("can't instantiate")   # can't instantiate