c17_mixins

Chapter 17: Mixins

Table of contents:

• Chapter 17: Mixins
  • Introduction to mixin
    • Example of a mixin

Introduction to mixin

Mixin is a class that adds method implementation. It is intended to be used to add method implementation but not instantiation so we generally add methods to the mixin class. Mixin uses a concept of multiple inheritance to combine all parent methods to create a new type by a child class.

We can implement multiple mixins in a child class to expand its usability and reduce code duplication. Python uses C3 Linearization or Method Resolution order to deal with collisions if there are same methods defined in multiple mixins. To know more about it, you can review the topic Multiple Inheritance.

Reference: https://en.wikipedia.org/wiki/C3_linearization

Example of a mixin

# resource/c17_mixins/example/ch1501_mixin.py
class Vehicle:
    """
    Base class
    """

    name: str

    def __init__(self, name: str) -> None:
        self.name = name


class EvMixin:
    """
    A mixin that adds more method implementation without affecting the parent's
    instantiation
    """

    name: str  # this mixin expects attribute `name` to be in the parent class

    def recharge_with_ac(self):
        assert self.name
        print(f"⚡: Recharging {self.name} with alternating current")

    def recharge_with_dc(self):
        print(f"⚡: Recharging {self.name} with direct current")


class ElectricCar(Vehicle, EvMixin):
    """
    A child class that inherits `Vehicle` and implements `EvMixin`.
    """

    def __init__(self, name: str) -> None:
        super().__init__(name)


if __name__ == "__main__":
    car = ElectricCar("my electric car")
    car.recharge_with_ac()
    car.recharge_with_dc()

Output

⚡: Recharging my electric car with alternating current
⚡: Recharging my electric car with direct current