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Python Programming Intermediate Level ~4 min read

Explain the SOLID principles in Object-Oriented Software Design with concise engineering examples.

Quick Revision Summary

SOLID (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) guides decoupled, extensible software design.

Interactive Practice Mode
Formulate your thoughts or take notes before revealing the model solution.
Model Answer & Deep-Dive Explanation

SOLID represents five fundamental design principles for maintainable, decoupled object-oriented architecture:

  1. Single Responsibility Principle (SRP): A class should have only one reason to change (e.g. separate invoice calculation from invoice PDF generation).
  2. Open/Closed Principle (OCP): Software entities should be open for extension, but closed for modification (e.g. add new discount strategies by subclassing rather than editing core billing logic).
  3. Liskov Substitution Principle (LSP): Subtypes must be substitutable for their base types without breaking program behavior.
  4. Interface Segregation Principle (ISP): Clients should not be forced to depend on interfaces they do not use; prefer many small, cohesive interfaces over one fat interface.
  5. Dependency Inversion Principle (DIP): High-level modules should depend on abstractions, not on concrete implementations (e.g. depend on PaymentGateway interface rather than RazorpayClient directly).

Interviewer Evaluation Points & Scoring Rubric

  • 1 1. Defines all 5 acronym letters accurately. 2. Provides concrete software engineering examples. 3. Explains how DIP enables unit testing and mock injection.
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