Day 40:Overusing inheritance instead of composition

 

🐍 Python Mistakes Everyone Makes ❌

Day 40: Overusing Inheritance Instead of Composition

Inheritance is one of the first OOP concepts most Python developers learn.
And that’s exactly why it’s often overused.

Just because you can inherit from a class doesn’t mean you should.

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❌ The Mistake

Using inheritance when the relationship is not truly “is-a”.

class Engine:
    def start(self):
        print("Engine started")

class Car(Engine): # ❌ Car is NOT an Engine
    def drive(self):

     print("Car is driving")

This design implies:

A Car is an Engine

Which is logically incorrect.

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❌ Why This Fails

• ❌ Creates tight coupling

• ❌ Makes the code harder to change later

• ❌ Breaks real-world modeling

• ❌ Leads to fragile inheritance hierarchies

• ❌ Prevents reusing components independently

If Engine changes, Car breaks.

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✅ The Correct Way: Composition

Use composition when an object has another object.

class Engine:
     def start(self):
         print("Engine started")

class Car:
    def __init__(self):
       self.engine = Engine() # ✅ Composition

 def drive(self):
    self.engine.start() 

      print("Car is driving")


Now:

A Car has an Engine

This is flexible, realistic, and scalable.

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🧠 Why Composition Wins

• Components can be swapped or upgraded

• Code becomes modular

• Easier testing and reuse

• Fewer breaking changes

• Cleaner mental model

Want an electric engine? Just replace it.

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🧠 Simple Rule to Remember

🧩 Use inheritance for “is-a” relationships
🔗 Use composition for “has-a” relationships

If it feels awkward to say out loud — it’s probably wrong in code too.

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🚀 Final Takeaway

Inheritance is powerful — but dangerous when misused.

Most real-world systems are built from parts, not types.
Favor composition first, and reach for inheritance only when the relationship is truly structural.

Good design is about flexibility, not clever hierarchies.