How to be a Django Form Mixologist

You’ve undoubtedly come across the Mixin pattern in Python: it allows for easy inheritance and a DRY method for code. However, the clean method makes things a bit tricky, especially when dealing with cleaning fields that depend on each other. This guide will show you how to properly implement a Django form with mixin classes.

Why Mixins?

Mixins are great for mixing multiple classes together. For example, consider the following example:

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

    def speak(self):
        raise NotImplementedError("Subclasses must implement this method")

class MammalMixin:
    def give_birth(self):
        return f"{self.name} gives birth."

class ReptileMixin:
    def lay_eggs(self):
        return f"{self.name} lays eggs."

class Lion(Animal, MammalMixin):
    pass

lion = Lion("Simba")
try:
    print(lion.speak())  # Raises NotImplementedError because it hasn't been implemented yet
except Exception as e:
    print(e)
print(lion.give_birth())  # Output: Simba gives birth.
try:
    print(lion.lay_eggs())   # Output: Simba cannot lay eggs.
except Exception as e…