Python Exception Handling

1. Purpose of Exception Handling

Exception handling prevents abrupt program termination and allows controlled recovery from runtime errors.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Handled division by zero safely")

Ensures stable application behavior.

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2. Basic try...except Structure

try:
    number = int("abc")
except ValueError:
    print("Invalid number format")

Separates risky code from error-handling logic.

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3. Handling Multiple Exceptions

try:
    value = int("10")
    result = value / 0
except ValueError:
    print("Conversion error")
except ZeroDivisionError:
    print("Division error")

Different exception types can be managed independently.

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4. Using try...except...else

try:
    num = int("50")
except ValueError:
    print("Conversion failed")
else:
    print("Conversion successful:", num)

else executes only if no exception occurs.

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5. Using try...except...finally

try:
    file = open("data.txt", "r")
except FileNotFoundError:
    print("File not found")
finally:
    print("Cleanup operations executed")

finally always runs, making it ideal for resource cleanup.

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6. Nested Exception Handling

try:
    try:
        x = int("abc")
    except ValueError:
        print("Inner exception handled")
except Exception:
    print("Outer exception handler")

Allows granular control over layered risky operations.

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7. Catching Generic Exceptions

try:
    risky_operation()
except Exception as e:
    print("Error:", e)

Catches all exceptions; useful for logging but should be used carefully.

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8. Re-raising Exceptions

try:
    value = int("xyz")
except ValueError:
    print("Logging error before re-raising")
    raise

Preserves the original traceback while adding contextual handling.

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9. Custom Exception Handling Strategy

class InvalidAgeError(Exception):
    pass

def validate_age(age):
    if age < 18:
        raise InvalidAgeError("Age must be 18 or above")

try:
    validate_age(16)
except InvalidAgeError as e:
    print(e)

Allows domain-specific error control.

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10. Production-Grade Exception Handling Pattern

def safe_divide(a, b):
    try:
        return a / b
    except ZeroDivisionError as e:
        return f"Error: {e}"
    except Exception as e:
        return f"Unexpected error: {e}"
    finally:
        print("Operation attempted")

print(safe_divide(10, 0))

Combines graceful handling, error reporting, and guaranteed execution logic.

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