Method overriding

Related code

class Animal:
    def __init__(self, name, age, energy):
        self.name = name
        self.age = age
        self.energy = energy

    def __str__(self):
        return f"{self.name} is {self.age} years old."

    def play(self, hours):
        self.energy -= hours * 10

    def sleep(self, hours):
        self.energy += hours * 10

Now we want to represent a goat, which also has a name, age, and energy, just like other animals. A goat can play and sleep, but unlike a dog or cat, it needs less sleep to regain energy. Specifically, a goat gains 20 units of energy per hour of sleep, compared to the usual 10 units in most animals.

To model this behavior, we create a Goat class that inherits from the Animal class. Then, we override the method that behaves differently, namely, the sleep method.

Method overriding happens when a child class defines a method with the same name as one in its parent class, but with a different implementation. When the method is called on an instance of the child class, the child's version is used, effectively replacing the parent's version for that instance.

...
class Goat(Animal):
    def sleep(self, hours):
        self.energy += hours * 20

>>> cuca = Goat("Cuca", 1, 50)
>>> cuca.play(1)
>>> cuca.energy
40
>>> cuca.sleep(1)
>>> cuca.energy
60

When a method is called on a Goat instance, Python first looks for that method inside the Goat class.
If it finds a method with that name, it executes it immediately.
If it doesn't find it in the Goat class, Python then continues the search in the parent class (Animal) and uses the first matching it finds there.