Errors

Exceptions

Use try, except, else, and finally to separate success, recovery, and cleanup.

When no exception is raised, the else block runs. Keeping success in else makes the try block contain only the operation that might fail.

Source

def parse_int(text):
    return int(text)

text = "42"
try:
    number = parse_int(text)
except ValueError:
    print(f"{text}: invalid")
else:
    print(f"{text}: {number}")
finally:
    print(f"checked {text}")

Output

42: 42
checked 42

When parsing fails, int() raises ValueError. Catching that specific exception makes the expected recovery path explicit.

Source

text = "python"
try:
    number = parse_int(text)
except ValueError:
    print(f"{text}: invalid")
else:
    print(f"{text}: {number}")
finally:
    print(f"checked {text}")

Output

python: invalid
checked python

Bare except: and broad except Exception: swallow far more than the failure you meant to handle, including KeyboardInterrupt (bare) and most programming bugs (broad). Catch the specific class — ValueError here — so unexpected failures still surface.

Source

def safe_parse_broken(text):
    try:
        return int(text)
    except Exception:
        return None

def safe_parse_fixed(text):
    try:
        return int(text)
    except ValueError:
        return None

print(safe_parse_broken("42"))
print(safe_parse_fixed("42"))

Output

42
42

Notes

Catch the most specific exception you can.
else is for success code that should run only if the try block did not fail.
finally runs whether the operation succeeded or failed.
Avoid bare except: and broad except Exception: — they hide bugs and absorb signals like KeyboardInterrupt.

Run the complete example

Expected output

42: 42
checked 42
python: invalid
checked python
42
42

Execution time appears here after you run the example.

Exceptions

See also

Run the complete example

Example code

Expected output