Debugging & Testing

Debugging is 50% of programming. Instead of just staring at code, learn to use print debugging effectively, or better yet, the Python Debugger (`pdb`). **Key Strategy**: Isolate the problem. Comment out code until you find the minimum crashing line.

Python
def complex_calc(x):
    # print(f"DEBUG: x={x}")  <-- Poor man's debugger
    import pdb; pdb.set_trace()  # Professional debugger
    return x * x

Python prefers **EAFP** (Easier to Ask Forgiveness than Permission). Instead of checking if a file exists (LBYL), just try to open it and catch the error. • **LBYL**: `if key in my_dict: val = my_dict[key]` • **EAFP**: `try: val = my_dict[key] except KeyError: ...` EAFP is often cleaner and faster in Python.

Python
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Oops, can't divide by zero!")
except Exception as e:
    print(f"Unexpected error: {e}")

Manual testing is slow and unreliable. `unittest` lets you write checks that run automatically. This is crucial for **Refactoring**—changing code structure without breaking behavior.

Python
import unittest

def add(a, b): return a + b

class TestMath(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(1, 2), 3)
        self.assertRaises(TypeError, add, 1, 'a')