🛡️ Defensive Programming¶

Defensive programming is about preventing errors before they happen. You validate inputs, check assumptions, and create clear guardrails so code fails fast and predictably.

✅ Common Defensive Techniques¶

Input validation: check types, ranges, and formats.
Guard clauses: return early for invalid states.
Assertions: verify internal assumptions.
Defaults: provide safe fallbacks.

✅ Example: Guard Clauses¶

def transfer(balance, amount):
    if amount <= 0:
        raise ValueError("Amount must be positive")
    if amount > balance:
        raise ValueError("Insufficient funds")
    return balance - amount

✅ Assertions (Internal Checks)¶

def average(values):
    assert values, "values must not be empty"
    return sum(values) / len(values)

Use assertions for programmer errors, not user input.

🔍 Key Takeaways¶

Validate inputs early and clearly.
Guard clauses keep code readable.
Assertions document internal assumptions.

Next: Logging →