📐 SOLID Principles Explained Like You're 5
Building AI systems and writing about how they actually work. Master of AI @ University of Technology Sydney. Previously B.Tech CS with focus on IoT. I believe the best way to learn is to explain. That's why I'm documenting tech concepts with simple analogies (@sreekarreddy.com). AWS Certified • Azure AI Certified • Neo4j Professional • Google Data Analytics When not coding: exploring Sydney, working on side projects, and teaching tech to anyone who'll listen.
Five rules for maintainable code
Day 115 of 149
👉 Full deep-dive with code examples
The LEGO Blocks Analogy
Good LEGO pieces:
- Do one thing well (a wheel is just a wheel)
- Can be extended without breaking
- Are interchangeable (any wheel fits any axle)
- Connect through standard interfaces
SOLID principles make code like well-designed LEGO - modular and maintainable.
The Five Principles
| Letter | Principle | Meaning |
| S | Single Responsibility | One class, one job |
| O | Open/Closed | Open for extension, closed for modification |
| L | Liskov Substitution | Subtypes must be substitutable |
| I | Interface Segregation | Many small interfaces beat one big one |
| D | Dependency Inversion | Depend on abstractions, not concretions |
Quick Examples
Single Responsibility
# Bad: User class does everything
class User:
def save(self): ...
def send_email(self): ...
def generate_report(self): ...
# Good: Separate responsibilities
class User: ...
class UserRepository: ...
class EmailService: ...
Dependency Inversion
# Bad: Hardcoded dependency
class UserService:
def __init__(self):
self.db = MySQLDatabase() # Locked in!
# Good: Inject abstraction
class UserService:
def __init__(self, database: Database):
self.db = database # Flexible!
Why It Matters
- Easier testing - Mock dependencies easily
- Easier changes - Modify one thing without breaking others
- Better collaboration - Clear boundaries between components
In One Sentence
SOLID principles guide object-oriented design toward flexible, maintainable, and testable code through five complementary rules.
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