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Mediator in Python

Mediator is a behavioral design pattern that reduces coupling between components of a program by making them communicate indirectly, through a special mediator object.

The Mediator makes it easy to modify, extend and reuse individual components because they’re no longer dependent on the dozens of other classes.



Usage examples: The most popular usage of the Mediator pattern in Python code is facilitating communications between GUI components of an app. The synonym of the Mediator is the Controller part of MVC pattern.

Conceptual Example

This example illustrates the structure of the Mediator design pattern. It focuses on answering these questions:

  • What classes does it consist of?
  • What roles do these classes play?
  • In what way the elements of the pattern are related? Conceptual example

from __future__ import annotations
from abc import ABC

class Mediator(ABC):
    The Mediator interface declares a method used by components to notify the
    mediator about various events. The Mediator may react to these events and
    pass the execution to other components.

    def notify(self, sender: object, event: str) -> None:

class ConcreteMediator(Mediator):
    def __init__(self, component1: Component1, component2: Component2) -> None:
        self._component1 = component1
        self._component1.mediator = self
        self._component2 = component2
        self._component2.mediator = self

    def notify(self, sender: object, event: str) -> None:
        if event == "A":
            print("Mediator reacts on A and triggers following operations:")
        elif event == "D":
            print("Mediator reacts on D and triggers following operations:")

class BaseComponent:
    The Base Component provides the basic functionality of storing a mediator's
    instance inside component objects.

    def __init__(self, mediator: Mediator = None) -> None:
        self._mediator = mediator

    def mediator(self) -> Mediator:
        return self._mediator

    def mediator(self, mediator: Mediator) -> None:
        self._mediator = mediator

Concrete Components implement various functionality. They don't depend on other
components. They also don't depend on any concrete mediator classes.

class Component1(BaseComponent):
    def do_a(self) -> None:
        print("Component 1 does A.")
        self.mediator.notify(self, "A")

    def do_b(self) -> None:
        print("Component 1 does B.")
        self.mediator.notify(self, "B")

class Component2(BaseComponent):
    def do_c(self) -> None:
        print("Component 2 does C.")
        self.mediator.notify(self, "C")

    def do_d(self) -> None:
        print("Component 2 does D.")
        self.mediator.notify(self, "D")

if __name__ == "__main__":
    # The client code.
    c1 = Component1()
    c2 = Component2()
    mediator = ConcreteMediator(c1, c2)

    print("Client triggers operation A.")

    print("\n", end="")

    print("Client triggers operation D.")

Output.txt: Execution result

Client triggers operation A.
Component 1 does A.
Mediator reacts on A and triggers following operations:
Component 2 does C.

Client triggers operation D.
Component 2 does D.
Mediator reacts on D and triggers following operations:
Component 1 does B.
Component 2 does C.

Mediator in Other Languages

Mediator in C# Mediator in C++ Mediator in Go Mediator in Java Mediator in PHP Mediator in Ruby Mediator in Rust Mediator in Swift Mediator in TypeScript