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🧱 Separation of Concerns

Separation of concerns (SoC) means organizing code so that each part focuses on a distinct responsibility. When responsibilities are mixed, changes become risky because unrelated behavior is tangled together.

✅ Common “Concerns” in Programs

  • Input/Output: CLI, HTTP, file reading/writing
  • Business logic: rules and computations
  • Data access: databases, APIs
  • Presentation: formatting, UI, reporting

âś… Why SoC Matters

  • Easier changes: UI changes don’t break business rules.
  • Better tests: business logic can be tested without I/O.
  • Cleaner boundaries: reduces coupling between parts.

âś… Example: Split I/O From Logic

Instead of mixing parsing + computation + printing:

def run():
    text = input("Enter numbers: ")
    nums = [int(x) for x in text.split(",")]
    print(sum(nums) / len(nums))

Separate concerns:

def parse_numbers(text):
    return [int(x) for x in text.split(",")]

def average(nums):
    return sum(nums) / len(nums)

def run():
    nums = parse_numbers(input("Enter numbers: "))
    print(average(nums))

🔍 Key Takeaways

  • Keep I/O at the edges; keep logic pure where possible.
  • Group related responsibilities together.
  • Boundaries make testing and refactoring safer.

Back: YAGNI Principle | Next: Coupling and Cohesion