except block does not catch the exception in python

Question

my code is like below

class Something(models.Model)

    def exception(self)
    try:
       Something.objects.all()
    except Exception():
       raise Exception()

called this method from testcases ,its working but i need to raise exception ,it does not catch the exception and here is my test case

def test_exception(self):
    instance = Something()
    instance.exception()

its working fine but i need to raise exception from except block

It is very unclear what you are trying to do. Why are you raising an exception from your catch-block? Also, there are numerous syntax-errors in your example (e.g. missing : and bad indentation on exception). — Björn Pollex
– Björn Pollex, Commented Oct 20, 2011 at 8:10
If you using the python unittest framework you probably wanna use the assertRaises(exception) method. — Nicola Coretti
– Nicola Coretti, Commented Oct 20, 2011 at 8:13

Nicola Musatti · Accepted Answer · 2011-10-20 08:09:58Z

8

This line:

except Exception():

should be:

except Exception:

answered Oct 20, 2011 at 8:09

Nicola Musatti

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3 Comments

Daniel Roseman Over a year ago

Yes, but of course it shouldn't be, as it's an extremely bad idea to just catch Exception - you should catch the actual exceptions you handle, and leave the others to bubble up.

Nicola Musatti Over a year ago

May I know the reason of the downvote? My reply is technically correct and answers exactly the OP question, so I see no justifiable reason for a downvote, see StackOverflow's FAQ. If you want to advise the OP about good Python programming practices, comment the question.

Vincenzooo Over a year ago

@nicola You are right. Indeed I upvoted it. It answer the question better than the other answers, which point out the right use, but not why the original example is failing. I suspect it should be also raise Exception (without parenthesis) or raise. good practice vs bad practice was not part of the question.

avasal · Accepted Answer · 2011-10-20 13:08:44Z

2

def exception(self)
    try:
        Something.objects.all()
    except Exception, err:
        #print err.message (if you want)
        raise err

This will catch the error and print the exact msg if required.

edited Oct 20, 2011 at 13:08

answered Oct 20, 2011 at 9:13

avasal

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1 Comment

Xion Over a year ago

I believe you meant raise err. You cannot raise err.message which is a string.

unutbu · Accepted Answer · 2011-10-20 08:47:07Z

Why catch the Exception just to re-raise it? If you are not doing anything in the except suite except re-raising the exception, then simply do not catch the exception in the first place:

@staticmethod
def exception():
    Something.objects.all()

If you are doing something nontrivial inside the except suite, then:

def exception(self):
    try:
        Something.objects.all()
    except Exception:
        # do something (with self?)
        raise

Then, to test that the exception method raises an Exception:

def test_exception(self):
    instance = Something()
    self.assertRaises(Exception, instance.exception)

This depends on Something.objects.all() raising Exception.

PS. If exception does not depend on self, then it is best to remove it from the argument list and make exception a staticmethod.

PPS. Exception is a very broad base exception class. A more specific exception would be more helpful for debugging, and allow other code to catch this specific exception instead of forcing it to handle any possible Exception.

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