Interface Segregation

The Interface Segregation Principle (ISP) is one of the SOLID principles of object-oriented design, emphasizing that a class should not be forced to implement interfaces it does not use. It promotes the idea of creating client-specific interfaces to prevent classes from being burdened with methods they do not need.

Key principles of the Interface Segregation Principle (ISP):

1. Client-Specific Interfaces:

   • Instead of creating large, general-purpose interfaces, design interfaces that are specific to the needs of the clients (classes or modules) that use them.
   • This ensures that each class is only obligated to implement the methods relevant to its specific requirements.

2. Avoidance of Fat Interfaces:

   • Fat interfaces contain more methods than a class might need, leading to unnecessary dependencies and potential implementation of irrelevant methods.
   • ISP suggests breaking down interfaces into smaller, focused ones, reducing the chance of forcing classes to implement unnecessary functionality.

3. Reduced Dependency:

   • By adhering to ISP, classes become less dependent on methods they don't use, reducing coupling between different parts of the system.
   • Reducing dependencies contributes to a more modular and maintainable codebase.

4. Flexibility in Implementations:

   • ISP allows for flexibility in implementing interfaces, enabling classes to implement only what is required for their specific functionality.
   • This flexibility promotes adaptability to changes and simplifies future modifications.

Example:

Consider a scenario where you have an Worker interface that includes methods for both manual and automated tasks. Without following ISP, a class like Robot may be forced to implement methods irrelevant to its nature.

# Without ISP
class Worker:
    def do_manual_work(self):
        pass

    def operate_machine(self):
        pass

class HumanWorker(Worker):
    def do_manual_work(self):
        # Human-specific manual work

    def operate_machine(self):
        # Human cannot operate a machine

class RobotWorker(Worker):
    def do_manual_work(self):
        # Robot does not perform manual work

    def operate_machine(self):
        # Robot-specific machine operation

Following ISP, we can create separate interfaces for manual work and machine operation, allowing classes to implement only the relevant methods:

# With ISP
class ManualWorker:
    def do_manual_work(self):
        pass

class MachineOperator:
    def operate_machine(self):
        pass

class HumanWorker(ManualWorker, MachineOperator):
    def do_manual_work(self):
        # Human-specific manual work

    def operate_machine(self):
        # Human-specific machine operation

class RobotWorker(MachineOperator):
    def operate_machine(self):
        # Robot-specific machine operation

Now, classes can implement only the interfaces that are relevant to their nature, adhering to the Interface Segregation Principle.