exceptions.md

Python by Example: Exceptions

Exceptions handle errors gracefully. Use try/except to catch them; use raise to signal them. else runs only when no exception occurred; finally always runs (e.g., for cleanup). Catch specific exception types when you can—avoid bare except: which catches everything including KeyboardInterrupt.

What you'll learn:

• try, except, else, finally
• Catching specific exceptions
• Raising exceptions with raise

try:
    result = 10 / 2
    print(result)
except ZeroDivisionError:
    print("Cannot divide by zero")
else:
    print("Division succeeded")
finally:
    print("Done")

# Raising exceptions
def get_item(lst, index):
    if index < 0 or index >= len(lst):
        raise IndexError(f"Index {index} out of range")
    return lst[index]

try:
    get_item([1, 2, 3], 10)
except IndexError as e:
    print(f"Caught: {e}")

except IndexError as e captures the exception object so you can inspect it. The else block runs only if no exception was raised in try. finally runs whether or not an exception occurred.

To run this program:

$ python source/exceptions.py
5.0
Division succeeded
Done
Caught: Index 10 out of range

Tip: Prefer specific exceptions (except ValueError) over broad ones (except Exception). It prevents masking bugs.

Try it: Wrap a division in try/except and handle both ZeroDivisionError and TypeError.

Source: exceptions.py

Next: Custom Exceptions