Practical example of mixins in python

mixin_patterns.py

"""
# Mixin

## Definition 
From https://en.wikipedia.org/wiki/Mixin

In object-oriented programming languages, a mixin (or mix-in)[1][2][3][4] is a class that contains methods for use by other classes without having to be the parent class of those other classes. How those other classes gain access to the mixin's methods depends on the language. Mixins are sometimes described as being "included" rather than "inherited".

"""
# Base case
class foo(object):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)


class bar(object):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2


class foobar(foo, bar):
    pass

# Pattern 1: define add on subclass (drawback: duplication of method in any further inherited)
class foo(object):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)


class bar(object):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2


class foobar(foo, bar):

    def add(self, num1, num2):
        return num1 + num2


# Pattern 2: define add on both foo and bar (drawback: duplication of method on base classes)
class foo(object):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)

    def add(self, num1, num2):
        return num1 + num2


class bar(object):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2

    def add(self, num1, num2):
        return num1 + num2


class foobar(foo, bar):
    pass


# Pattern 3: define add on one of foo or bar (drawback: unintuitive, duplication of method on subbar
class foo(object):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)

    def add(self, num1, num2):
        return num1 + num2

class bar(object):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2


class foobar(foo, bar):
    pass


class subfoo(foo):
    pass


class subbar(bar):

    def add(self, num1, num2):
        return num1 + num2


# Pattern 4: define common base class (not a mixin pattern) (drawbacks: hidden complexity)

class add(object):
    def add(self, num1, num2):
        return num1 + num2


class foo(add):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)


class bar(add):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2


class foobar(foo, bar):
    pass


class subfoo(foo):
    pass


class subbar(bar):
    pass


# Pattern 5: define add class as mixin inherited by child class (drawbacks: front-loading of dependencies, unintuitive, any child class without 'add' dependency will suffer runtime error)

class add(object):
    def add(self, num1, num2):
        return num1 + num2


class foo(object):
    total = 0

    def get_total(self, num1, num2):
        self.total = self.add(num1, num2)


class bar(object):
    mean = 0

    def get_mean(self, num1, num2):
        self.mean = self.add(num1, num2) / 2


class foobar(foo, bar, add):
    pass


class subfoo(foo, add):
    pass


class subbar(bar, add):
    pass