{"id":2760,"date":"2021-11-07T09:34:33","date_gmt":"2021-11-07T09:34:33","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=2760"},"modified":"2025-03-28T03:26:40","modified_gmt":"2025-03-28T03:26:40","slug":"python-mixin","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-oop\/python-mixin\/","title":{"rendered":"Python mixin"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python mixin classes and how to use them to make the code reusable.<\/p>\n\n\n\n

What is a mixin in Python #<\/a><\/h2>\n\n\n\n

A mixin is a class<\/a> that provides method implementations for reuse by multiple related child classes. However, the inheritance is not implying an is-a relationship.<\/p>\n\n\n\n

A mixin doesn’t define a new type. Therefore, it is not intended for direct instantiation.<\/p>\n\n\n\n

A mixin bundles a set of methods<\/a> for reuse. Each mixin should have a single specific behavior, implementing closely related methods.<\/p>\n\n\n\n

Typically, a child class uses multiple inheritance<\/a> to combine the mixin classes with a parent class.<\/p>\n\n\n\n

Since Python doesn’t define a formal way to define mixin classes, it’s a good practice to name mixin classes with the suffix Mixin<\/code>.<\/p>\n\n\n\n

A mixin class is like an interface in Java<\/a> and C#<\/a> with implementation. And it’s like a trait in PHP<\/a>.<\/p>\n\n\n\n

Python mixin example #<\/a><\/h2>\n\n\n\n

First, define a Person<\/code> class:<\/p>\n\n\n

class<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name)<\/span>:<\/span>\n        self.name = name<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define an Employee<\/code> class that inherits from the Person<\/code> class:<\/p>\n\n\n
class<\/span> Employee<\/span>(Person)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, skills, dependents)<\/span>:<\/span>\n        super().__init__(name)\n        self.skills = skills\n        self.dependents = dependents<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, create a new instance of the Employee<\/code> class:<\/p>\n\n\n
if<\/span> __name__ == '__main__'<\/span>:\n    e = Employee(\n        name='John'<\/span>,\n        skills=['Python Programming'<\/span>'Project Management'<\/span>],\n        dependents={'wife'<\/span>: 'Jane'<\/span>, 'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>]}\n    )<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
However, you may want to convert objects of other classes to dictionaries<\/a>. To make the code reusable, you can define a mixin class called DictMixin<\/code> like the following:<\/p>\n\n\n
class<\/span> DictMixin<\/span>:<\/span>\n    def<\/span> to_dict<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._traverse_dict(self.__dict__)\n\n    def<\/span> _traverse_dict<\/span>(self, attributes: dict)<\/span> -> dict:<\/span>\n        result = {}\n        for<\/span> key, value in<\/span> attributes.items():\n            result[key] = self._traverse(key, value)\n\n        return<\/span> result\n\n    def<\/span> _traverse<\/span>(self, key, value)<\/span>:<\/span>\n        if<\/span> isinstance(value, DictMixin):\n            return<\/span> value.to_dict()\n        elif<\/span> isinstance(value, dict):\n            return<\/span> self._traverse_dict(value)\n        elif<\/span> isinstance(value, list):\n            return<\/span> [self._traverse(key, v) for<\/span> v in<\/span> value]\n        elif<\/span> hasattr(value, '__dict__'<\/span>):\n            return<\/span> self._traverse_dict(value.__dict__)\n        else<\/span>:\n            return<\/span> value<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The DictMixin<\/code> class has the to_dict()<\/code> method that converts an object to a dictionary.<\/p>\n\n\n\n
The _traverse_dict()<\/code> method iterates the object’s attributes and assigns the key and value to the result.<\/p>\n\n\n\n
The attribute of an object may be a list, a dictionary, or an object with the __dict__<\/code> attribute. Therefore, the _traverse_dict()<\/code> method uses the _traverse()<\/code> method to convert the attribute to value.<\/p>\n\n\n\n
To convert instances of the Employee<\/code> class to dictionaries, the Employee<\/code> needs to inherit from both DictMixin<\/code> and Person<\/code> classes:<\/p>\n\n\n
class<\/span> Employee<\/span>(DictMixin, Person)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, skills, dependents)<\/span>:<\/span>\n        super().__init__(name)\n        self.skills = skills\n        self.dependents = dependents<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you need to specify the mixin classes before other classes.<\/p>\n\n\n\n
The following creates a new instance of the Employee<\/code> class and converts it to a dictionary:<\/p>\n\n\n
e = Employee(\n    name='John'<\/span>,\n    skills=['Python Programming'<\/span>, 'Project Management'<\/span>],\n    dependents={'wife'<\/span>: 'Jane'<\/span>, 'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>]}\n)\n\npprint(e.to_dict())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
{'dependents'<\/span>: {'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>], 'wife'<\/span>: 'Jane'<\/span>},\n'name'<\/span>: 'John'<\/span>,\n'skills'<\/span>: ['Python Programming'<\/span>, 'Project Management'<\/span>]}<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following shows the complete code:<\/p>\n\n\n
from<\/span> pprint import<\/span> pprint\n\n\nclass<\/span> DictMixin<\/span>:<\/span>\n    def<\/span> to_dict<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._traverse_dict(self.__dict__)\n\n    def<\/span> _traverse_dict<\/span>(self, attributes)<\/span>:<\/span>\n        result = {}\n        for<\/span> key, value in<\/span> attributes.items():\n            result[key] = self._traverse(key, value)\n\n        return<\/span> result\n\n    def<\/span> _traverse<\/span>(self, key, value)<\/span>:<\/span>\n        if<\/span> isinstance(value, DictMixin):\n            return<\/span> value.to_dict()\n        elif<\/span> isinstance(value, dict):\n            return<\/span> self._traverse_dict(value)\n        elif<\/span> isinstance(value, list):\n            return<\/span> [self._traverse(key, v) for<\/span> v in<\/span> value]\n        elif<\/span> hasattr(value, '__dict__'<\/span>):\n            return<\/span> self._traverse_dict(value.__dict__)\n        else<\/span>:\n            return<\/span> value\n\n\nclass<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name)<\/span>:<\/span>\n        self.name = name\n\n\nclass<\/span> Employee<\/span>(DictMixin, Person)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, skills, dependents)<\/span>:<\/span>\n        super().__init__(name)\n        self.skills = skills\n        self.dependents = dependents\n\n\nif<\/span> __name__ == '__main__'<\/span>:\n    e = Employee(\n        name='John'<\/span>,\n        skills=['Python Programming'<\/span>, 'Project Management'<\/span>],\n        dependents={'wife'<\/span>: 'Jane'<\/span>, 'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>]}\n    )\n\n    pprint(e.to_dict())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Compose multiple mixin classes #<\/a><\/h2>\n\n\n\n
Suppose you want to convert the Employee<\/code>‘s object to JSON. To do that, you can first define a new mixin class that use the json<\/code> standard module:<\/p>\n\n\n
import<\/span> json\n\nclass<\/span> JSONMixin<\/span>:<\/span>\n    def<\/span> to_json<\/span>(self)<\/span>:<\/span>\n        return<\/span> json.dumps(self.to_dict())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And then change the Employee<\/code> class so that it inherits the JSONMixin<\/code> class:<\/p>\n\n\n
class<\/span> Employee<\/span>(DictMixin, JSONMixin, Person)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, skills, dependents)<\/span>:<\/span>\n        super().__init__(name)\n        self.skills = skills\n        self.dependents = dependents<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following creates a new instance of the Employee<\/code> class and converts it to a dictionary and json:<\/p>\n\n\n
if<\/span> __name__ == '__main__'<\/span>:\n    e = Employee(\n        name='John'<\/span>,\n        skills=['Python Programming'<\/span>'Project Management'<\/span>],\n        dependents={'wife'<\/span>: 'Jane'<\/span>, 'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>]}\n    )\n\n    pprint(e.to_dict())\n    print(e.to_json())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
{'dependents'<\/span>: {'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>], 'wife'<\/span>: 'Jane'<\/span>},\n'name'<\/span>: 'John'<\/span>,\n'skills'<\/span>: ['Python ProgrammingProject Management'<\/span>]}\n\n{\"name\"<\/span>: \"John\"<\/span>, \"skills\"<\/span>: [\"Python ProgrammingProject Management\"<\/span>], \"dependents\"<\/span>: {\"wife\"<\/span>: \"Jane\"<\/span>, \"children\"<\/span>: [\"Alice\"<\/span>, \"Bob\"<\/span>]}}<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following shows the complete code:<\/p>\n\n\n
import<\/span> json\nfrom<\/span> pprint import<\/span> pprint\n\n\nclass<\/span> DictMixin<\/span>:<\/span>\n    def<\/span> to_dict<\/span>(self)<\/span>:<\/span>\n        return<\/span> self._traverse_dict(self.__dict__)\n\n    def<\/span> _traverse_dict<\/span>(self, attributes)<\/span>:<\/span>\n        result = {}\n        for<\/span> key, value in<\/span> attributes.items():\n            result[key] = self._traverse(key, value)\n\n        return<\/span> result\n\n    def<\/span> _traverse<\/span>(self, key, value)<\/span>:<\/span>\n        if<\/span> isinstance(value, DictMixin):\n            return<\/span> value.to_dict()\n        elif<\/span> isinstance(value, dict):\n            return<\/span> self._traverse_dict(value)\n        elif<\/span> isinstance(value, list):\n            return<\/span> [self._traverse(key, v) for<\/span> v in<\/span> value]\n        elif<\/span> hasattr(value, '__dict__'<\/span>):\n            return<\/span> self._traverse_dict(value.__dict__)\n        else<\/span>:\n            return<\/span> value\n\n\nclass<\/span> JSONMixin<\/span>:<\/span>\n    def<\/span> to_json<\/span>(self)<\/span>:<\/span>\n        return<\/span> json.dumps(self.to_dict())\n\n\nclass<\/span> Person<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name)<\/span>:<\/span>\n        self.name = name\n\n\nclass<\/span> Employee<\/span>(DictMixin, JSONMixin, Person)<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, name, skills, dependents)<\/span>:<\/span>\n        super().__init__(name)\n        self.skills = skills\n        self.dependents = dependents\n\n\nif<\/span> __name__ == '__main__'<\/span>:\n    e = Employee(\n        name='John'<\/span>,\n        skills=['Python Programming'<\/span>'Project Management'<\/span>],\n        dependents={'wife'<\/span>: 'Jane'<\/span>, 'children'<\/span>: ['Alice'<\/span>, 'Bob'<\/span>]}\n    )\n\n    pprint(e.to_dict())\n    print(e.to_json())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • A mixin class provides method implementions for resuse by multiple related subclasses.<\/li>\n<\/ul>\n
    \n\t
    \n\t\t
    Was this tutorial helpful ?<\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
    \n\t\t
    \n\t\t\t
    <\/div>\n\t\t\t
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Suppose you want to convert the Employee<\/code> object to a dictionary<\/a>. To do that, you can add a new method to the Employee<\/code> class, which converts the object to a dictionary.<\/p>\n\n\n\n