Mediator Method - Python Design Pattern

Mediator Method is a Behavioral Design Pattern that allows us to reduce the unordered dependencies between the objects. In a mediator environment, objects take the help of mediator objects to communicate with each other. It reduces coupling by reducing the dependencies between communicating objects. The mediator works as a router between objects and it can have it’s own logic to provide a way of communication.

Design Components:

• Mediator: It defines the interface for communication between colleague objects.
• Concrete Mediator: It implements the mediator interface and coordinates communication between colleague objects.
• Colleague: It defines the interface for communication with other colleagues
• Concrete Colleague: It implements the colleague interface and communicates with other colleagues through its mediator.

Problem Without using Mediator Method

Imagine you are going to take admission in one of the elite courses offered by GeeksforGeeks such as DSA, SDE, and STL. Initially, there are very few students who are approaching to join these courses. Initially, the developer can create separate objects and classes for the connection between the students and the courses but as the courses become famous among students it becomes hard for developers to handle such a huge number of sub-classes and their objects.

Solution using Mediator Method

Now let us understand how a pro developer will handle such a situation using the Mediator design pattern. We can create a separate mediator class named as Course and a User Class using which we can create different objects of Course class. In the main method, we will create a separate object for each student and inside the User class, we will create the object for Course class which helps in preventing the unordered code.

class Course(object):
    """Mediator class."""

    def displayCourse(self, user, course_name):
        print("[{}'s course ]: {}".format(user, course_name))


class User(object):
    '''A class whose instances want to interact with each other.'''

    def __init__(self, name):
        self.name = name
        self.course = Course()

    def sendCourse(self, course_name):
        self.course.displayCourse(self, course_name)

    def __str__(self):
        return self.name

"""main method"""

if __name__ == "__main__":

    mayank = User('Mayank')   # user object
    lakshya = User('Lakshya') # user object
    krishna = User('Krishna') # user object

    mayank.sendCourse("Data Structures and Algorithms")
    lakshya.sendCourse("Software Development Engineer")
    krishna.sendCourse("Standard Template Library")

UML Diagram

Following is the UML Diagram for Mediator Method:

Advantages

• Single Responsibility Principle: Extracting the communications between the various components is possible under Mediator Method into a single place which is easier to maintain.
• Open/Closed Principle: It's easy to introduce new mediators without disturbing the existing client code.
• Allows Inheritance: We can reuse the individual components of the mediators as it follows the Inheritance
• Few Sub-Classes: Mediator limits the Sub-Classing as a mediator localizes the behavior that otherwise would be disturbed among the several objects.

Disadvantages

• Centralization: It completely centralizes the control because the mediator pattern trades complexity of interaction for complexity in the mediator.
• God Object: A Mediator can be converted into a God Object (an object that knows too much or does too much).
• Increased Complexity: The structure of the mediator object may become too much complex if we put too much logic inside it.

Applicability

• Reduce the number of sub-classes: When you have realized that you have created a lot of unnecessary sub-classes, then it is preferred to use the Mediator method to avoid these unnecessary sub-classes.
• Air Traffic Controller: Air traffic controller is a great example of a mediator pattern where the airport control room works as a mediator for communication between different flights.

Further Read - Mediator Method in Java