Python · Chapter 27 of 45

Python Exceptions

Errors that happen at runtime are called EXCEPTIONS. Handle them with `try` / `except` so your program doesn't crash.

Add `else` (runs when no error) and `finally` (always runs) blocks as needed.

Syntax

try:
    risky()
except SomeError as e:
    handle(e)
finally:
    cleanup()

Catching specific errors

Catch the narrowest exception you can handle. Avoid bare `except:` — it hides bugs.

Use `raise ValueError('message')` to signal an error yourself.

Example 1 (python)

try:
    x = int("abc")
except ValueError as e:
    print("Bad number:", e)

Output

Bad number: invalid literal for int() with base 10: 'abc'

Catch a ValueError from a failed int() conversion.

Example 2 (python)

try:
    result = 10 / 0
except ZeroDivisionError:
    result = None
print(result)

Output

None

Handle division by zero gracefully.

💡 Note: Never use `except: pass` — silently swallowing errors is one of the top causes of hard-to-find bugs.