raise로 하위 에러 그대로 넘기기

try-except 문에서 except를 as로 받지 않고 그냥 raise하면 try문에서 발생했던 에러를 그대로 일으킨다.하위 두 코드는 같다.

In [1]: try:
   ...:     Notification.objects.get(id=3434)
   ...: except Notification.DoesNotExist as e:
   ...:     raise e
   ...:
DoesNotExist: Notification matching query does not exist.

In [1]: try:
   ...:     Notification.objects.get(id=3434)
   ...: except Notification.DoesNotExist:
   ...:     raise
   ...:
DoesNotExist: Notification matching query does not exist.

경우 실험

1. 그대로 raise

>>> try:
...     1 / 0
... except ZeroDivisionError:
...     raise
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

1. as e

>>> try:
...     1 / 0
... except ZeroDivisionError as e:
...     raise ValueError(e)
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
ValueError: division by zero

>>> try:
...     1 / 0
... except ZeroDivisionError as e:
...     raise ValueError(e) from e
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
ValueError: division by zero

1. custom message

>>> try:
...     1 / 0
... except ZeroDivisionError as e:
...     raise ValueError('ERROR!')
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
ValueError: ERROR!

>>> try:
...     1 / 0
... except ZeroDivisionError as e:
...     raise ValueError('ERROR!') from e
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
ValueError: ERROR!