all Python 3Exceptionsconstruct

try / except

handling

The try block holds code that may raise an exception. except catches it. else runs if there was none. finally runs always.

Syntax

try:
    ...
except ErrorType:
    ...

Catch the specific class: except Exception — and a bare except: even more so — also swallows typos like NameError and turns a bug into a program that quietly does the wrong thing, while a bare except: additionally grabs BaseException, KeyboardInterrupt and SystemExit included. Branch order matters, since the first matching handler wins: except Exception placed before except ValueError makes the later branch unreachable. Keep the try body as small as possible — the more lines it covers, the easier it is to catch an error you never meant to handle.

Examples

try:
    x = 1 / 0
except ZeroDivisionError:
    print('division by zero')  # → division by zero

try:
    int('abc')
except ValueError as e:
    print(e)  # → invalid literal for int() with base 10: 'abc'

# Несколько except: срабатывает первый подходящий
try:
    lst = [1, 2, 3]
    print(lst[10])
except IndexError:
    print('index error')  # → index error
except Exception as e:
    print('other:', e)

# else — если исключений не было
try:
    result = 10 / 2
except ZeroDivisionError:
    print('error')
else:
    print(result)  # → 5.0

# finally — выполняется всегда
try:
    f = open('/nonexistent')
except FileNotFoundError:
    print('not found')  # → not found
finally:
    print('always')  # → always

# Несколько типов в одном except
try:
    x = int(None)
except (TypeError, ValueError) as e:
    print(type(e).__name__)  # → TypeError

# Exception ловит всё, кроме SystemExit, KeyboardInterrupt и GeneratorExit
try:
    raise RuntimeError('oops')
except Exception as e:
    print(type(e).__name__, e)  # → RuntimeError oops

try / except

Syntax

Examples

See also