Lanzamiento y relanzamiento de excepciones

Introducción

Lanzar una excepción integrada

def divide(a, b):
    if b == 0:
        raise ValueError('Denominator cannot be zero')
    return a / b
try:
    divide(5, 0)
except ValueError as e:
    print(e)

Volver a lanzar la misma excepción

def process(data):
    try:
        return int(data)
    except ValueError:
        print('logging error')
        raise  # re-raises original
try:
    process('abc')
except ValueError:
    print('caller caught it')

Encadenar excepciones con from

try:
    int('abc')
except ValueError as original:
    raise RuntimeError('processing failed') from original

Suprimir el encadenamiento

try:
    int('abc')
except ValueError:
    raise RuntimeError('clean error') from None

Sentencia assert

def sqrt(x):
    assert x >= 0, f'Input must be non-negative, got {x}'
    return x ** 0.5
try:
    sqrt(-1)
except AssertionError as e:
    print(e)

Lanzamiento condicional

def process(items):
    if not items:
        raise ValueError('items must not be empty')
    return items[0]
print(process([1, 2, 3]))

Volver a lanzar frente a lanzar una excepción nueva

def outer():
    try:
        inner()
    except ValueError as e:
        raise RuntimeError('outer failed') from e
def inner():
    raise ValueError('inner failed')
try:
    outer()
except RuntimeError as e:
    print(e, e.__cause__)

Excepción en finally

try:
    try:
        raise ValueError('original')
    finally:
        print('finally ran')
except ValueError as e:
    print('caught:', e)

warnings.warn frente a raise

import warnings
def old_func():
    warnings.warn('Deprecated', DeprecationWarning)
    return 42
print(old_func())

Patrón raise from None

class DBError(Exception): pass
def query(q):
    try:
        raise ConnectionError('refused')
    except ConnectionError:
        raise DBError('query failed') from None
try:
    query('SELECT 1')
except DBError as e:
    print(e)

Comprobación rápida

Resumen

Siga avanzando