Python Mixins

While I pair with coworker, we get to read about Python mixins. I was aware of the existence of mixins but I haven’t actually read about them in details so it was a good opportunity for me to learn.

What is mixins in Python?

A mixin is a class that provides method implementations for reuse by multiple related child classes, specifically methods that child classes can utilize with. A mixin class is not considered a base class itself nor intended for direct instantiation. Typically, a child class that inherits the mixin class uses multiple inheritance. Since Python doesn’t have a formal way of defining mixin classes, it’s a good practice to name mixin classes with the suffix Mixin.

Example

This example is from pythontutorial.net.

Define a Person class:

class Person:
    def __init__(self, name):
        self.name = name

Define an Employee class that inherits from the Person class:

class Employee(Person):
    def __init__(self, name, skills, dependents):
        super().__init__(name)
        self.skills = skills
        self.dependents = dependents

Create an instance of the Employee class:

if __name__ == '__main__':
    e = Employee(
        name='John',
        skills=['Pythoning Programming'],
        dependents={'wife': 'Jane', 'children': ['Bob']}
    )

Now, if we want to convert Employee object to a dictionary, we can add a new method for doing that. However, if we want to convert objects of other classes to a dictionary as well, we can do it through mixins which allow us reuse code for different classes.

For instance, we can create a mixin class called DictMixin:

class DictMixin:
    def to_dict(self):
        return self._traverse_dict(self.__dict__)

    ...

Now that we have DictMixin, our Employee class can inherit from it to use to_dict() method:

class Employee(DictMixin, Person):
    def __init__(self, name, skills, dependents):
        super().__init__(name)
        self.skills = skills
        self.dependents = dependents

if __name__ == '__main__':
    e = Employee(
        name='John',
        skills=['Pythoning Programming'],
        dependents={'wife': 'Jane', 'children': ['Bob']}
    )
    e.to_dict()

note: we need to specify the mixin classes before other classes.

References

• pythontutorial.net, realpython.com