Mixin in Python 3.10

Mixin is a concept in object-oriented programming where a class can reuse code from another class without inheriting from it. Python 3.10 introduces a new syntax for using mixins called case. Here's an example of how to use mixins in Python 3.10:

from typing import Type, Protocol
class Loggable(Protocol):

    def log(self, message: str):

        ...
def with_logging(cls: Type):

    class Logged(cls):

        def log(self, message):

            print(f"{self.__class__.__name__}: {message}")

    return Logged
@with_logging

class MyClass:

    def foo(self):

        pass
my_object = MyClass()

my_object.log("Hello, world!")

In this example, we define a Loggable protocol that declares a log method. We then define a with_logging function that takes a class and returns a new class that inherits from the original class and adds a log method that prints out a message. We use Python 3.10's new case syntax to decorate the MyClass definition with the with_logging function.

Finally, we create an instance of MyClass and call the log method on it, which was added by the with_logging mixin. The output of this code will be:

MyClass: Hello, world!

So we can see that by using a mixin, we have added behavior to an existing class without having to modify the class directly.