🔗 Coupling and Cohesion

Two big design qualities:

• Coupling: how strongly one part depends on another.
• Cohesion: how well the responsibilities inside a part belong together.

Great designs aim for low coupling and high cohesion.

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✅ Low Coupling

Low coupling means components can change independently.

Signs of high coupling:

• Many imports and cross-calls between modules
• One small change forces changes in many places
• Code can’t be reused without dragging dependencies along

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✅ High Cohesion

High cohesion means a module/class/function does one focused job.

Signs of low cohesion:

• “Utility” modules that contain unrelated helpers
• Classes with many unrelated methods
• Functions that do validation + parsing + storage + formatting

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✅ Example: Improve Cohesion

Before (mixed responsibilities):

def process_order(order):
    validate(order)
    save_to_db(order)
    send_email(order)
    print("Done")

After (clear responsibilities):

def validate_order(order):
    ...

def persist_order(order):
    ...

def notify_order_created(order):
    ...

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🔍 Key Takeaways

• Low coupling reduces “blast radius” of change.
• High cohesion makes code easier to locate and reason about.
• SoC often improves both coupling and cohesion.

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