Home > Python Exception > Python Error Class

Python Error Class


Because if the message changes, then I have to change the exception check everywhere. def __init__(self, message): ... except NelsonsExceptions: ... Ugh. Check This Out

In any case, you only need the __init__ or __str__ if you do something different from what Exception itself does. How do I install the latest OpenOffice? Also, you can at least provide a docstring (and not be forced to use the pass keyword): class MyAppValueError(ValueError): '''Raise when my specific value is wrong''' Set attributes you create yourself So if you have def myfunction(*args), you can call it like myfunction("foo") or myfunction("foo", "bar") and the arguments will be accessible in the body of the function as the tuple args. https://docs.python.org/2.7/tutorial/errors.html

Python Custom Exception

Generating a sequence of zeros at compile time Half the pentagon! Join them; it only takes a minute: Sign up Manually raising (throwing) an exception in Python up vote 800 down vote favorite 189 How can I raise an exception in Python current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list.

asked 6 years ago viewed 504628 times active 1 month ago Blog Stack Overflow Podcast #92 - The Guerilla Guide to Interviewing Linked 9 How do I import FileNotFoundError from Python def __str__(self): return ': '.join(self.args) and you'll have >>> raise nastyerr('code is broken') NastyError: bad thing happened: code is broken share|improve this answer answered Aug 7 '13 at 16:23 mykhal 8,82054668 Prove sets equality. Python Exception Class Methods For example: try: some_code_that_may_raise_our_value_error() except ValueError as err: print(err.args) prints ('message', 'foo', 'bar', 'baz') In Python 2.5, an actual message attribute was added to BaseException in favor of encouraging users to

Should two DFAs be complete before making an intersection of them? Python Exception Message For future posterity: PEP 0352's sample code for BaseException shows exactly what's going on with args, __str()__, etc. –Nelson Aug 24 '09 at 14:19 45 Generaly I believe it would My primary goal is to follow whatever standard other exception classes have, so that (for instance) any extra string I include in the exception is printed out by whatever tool caught But you shouldn't error check that way because assertions can be turned off (python -O). –Two-Bit Alchemist Sep 16 '15 at 21:33 @Two-BitAlchemist Good point.

But in your case, did you consider ModelNotLoadedError as a type of LookupError? –Aaron Hall Feb 3 '15 at 21:16 1 Thanks! Python Print Exception Jokes about Monica's haircut Why does a full moon seem uniformly bright from earth, shouldn't it be dimmer at the "border"? EnvironmentError(2, 'foo', 'bar').errno returns 2 –Aaron Hall Aug 7 '15 at 18:46 add a comment| up vote 567 down vote DON'T DO THIS. Not the answer you're looking for?

Python Exception Message

If you want more flexibiilty from the exception, you could pass a dictionary as the argument: raise MyException({"message":"My hovercraft is full of animals", "animal":"eels"}) However, to get at those details in http://stackoverflow.com/questions/1319615/proper-way-to-declare-custom-exceptions-in-modern-python more hot questions question feed lang-py about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture / Recreation Python Custom Exception share|improve this answer edited Feb 27 '15 at 17:20 Zero Piraeus 17.6k125899 answered Jan 12 '10 at 21:08 Gabriel Hurley 24.6k94578 4 But now how do you catch this exception? Python Raise Valueerror It's interesting to know that the arguments passed to the constructor can be retrieved in the args attribute (it's a tuple). –Bastien Léonard Aug 23 '09 at 22:01 1 Hmm,

I was tripped up by the following deprecation warning in Python 2.6.2: >>> class MyError(Exception): ... his comment is here This works in Python 2 and 3. How do I find out if there is an Esperanto club in my city? self.errors = errors That way you could pass dict of error messages to the second param, and get to it later with e.errors share|improve this answer edited Oct 11 '14 at Python Exception Stack Trace

Browse other questions tagged python exception exception-handling or ask your own question. arguments as any other builtin Error super(MyAppValueError, self).__init__(message, foo, *args) There's really no need to write your own __str__ or __repr__. Cant find the game to this melody. this contact form This talk elaborates the topic: youtu.be/o9pEzgHorH0?t=9m56s (sorry for directing out of the declaration details). –dmitry_romanov Nov 27 '14 at 12:02 | show 1 more comment 6 Answers 6 active oldest votes

up vote 595 down vote favorite 158 What's the proper way to declare custom exception classes in modern Python? Python Filenotfounderror You can preserve the stacktrace (and error value) with sys.exc_info(), but this is way more error prone, prefer to use a bare raise to reraise. Utku ALTINKAYA 1,6821626 add a comment| up vote 4 down vote No, "message" is not forbidden.

And by "custom" I mean an Exception object that can include extra data about the cause of the error: a string, maybe also some other arbitrary object relevant to the exception.

  1. The correct answer is Aaron Hall's one. –David Wallace Feb 16 '15 at 9:38 | show 1 more comment up vote 15 down vote For the common case where you need
  2. But simply calling the message variable something else than message does the trick.
  3. When in except clause When inside an except clause, you might want to, e.g.
  4. If you really want an AssertionError in this case, write assert distance > 0, 'Distance must be positive'.
  5. In many similar cases it's a condition that isn't associated with a particular value.
  6. Something about Nintendo and Game Over Screen Hotel cancellation from booking.com Why don't browser DNS caches mitigate DDOS attacks on DNS providers?
  7. But you may want to get rid of the deprecation error, of course.
  8. Why do neural network researchers care about epochs?
  9. share|improve this answer edited Aug 23 '09 at 22:10 Bastien Léonard 31.3k106181 answered Aug 23 '09 at 21:46 M.

python exception exception-handling share|improve this question edited Feb 3 '15 at 14:37 DavidRR 5,20472747 asked Jan 12 '10 at 21:07 TIMEX 41.2k201525826 add a comment| 3 Answers 3 active oldest votes Why do jet engines smoke? Why do jet engines smoke? Python Catch Multiple Exceptions If I need to override __init__ for some reason, what's the right way to fill *args? –Nelson Aug 23 '09 at 22:06 15 +1.

Basically, __init__ is setting self.args = args. –Jeff Bradberry Aug 23 '09 at 22:20 1 Critique of top answer here: stackoverflow.com/a/26938914/541136 –Aaron Hall Nov 14 '14 at 22:23 2 class NastyError(ExceptionTemplate): pass and if you don't like that default tuple-like representation, just add __str__ method to the ExceptionTemplate class, like: # ... raise ValueError('A very specific bad thing happened') which also handily allows an arbitrary number of arguments to be passed to the constructor. http://vealcine.com/python-exception/python-standard-error-class.php Can you chain Tempestuous magic and War Caster?

raise ValueError('A very specific bad thing happened', 'foo', 'bar', 'baz') These arguments are accessed by the args attribute on the Exception object. don't do this. And if you have many exceptions in your application it's usually a good idea to have a common custom base class for all of them, so that users of your modules That's an interesting constraint that future users may not appreciate.

The idea was lost in simplification, when I wrote the simple example above. I'll demonstrate both errors: >>> ValidationError('foo', 'bar', 'baz').message Traceback (most recent call last): File "", line 1, in ValidationError('foo', 'bar', 'baz').message TypeError: __init__() takes exactly 3 arguments (4 given) >>> python.org/dev/peps/pep-0352 shows what is going on behind the scenes with current Exceptions. This removes the potential to be specific about what you catch.

Be specific in your message, e.g.: raise ValueError('A very specific bad thing happened') Don't do this: Avoid raising a generic Exception, to catch it, you'll have to catch all other more except Exception("I know python!") doesn't work. –Jason Axelson Sep 7 '11 at 5:01 40 @JasonAxelson catch this with "except Exception as e:". "except" cannot discriminate on the exception message, but I'm also fuzzily aware that Exception has some magic parameter args, but I've never known how to use it. Antsy permutations How can a nine tailed fox catch its prey?

Flight between non-Schengen countries with Schengen connection after exhausting 90/180 limit What is the purpose of diodes in flip-dot displays? Would it be ok to eat rice using spoon in front of Westerners? Hiding bugs raise Exception('I know Python!') # don't, if you catch, likely to hide bugs. From Python Exceptions: The base class for all built-in exceptions.

Will change it tomorrow –Alvaro Feb 4 '15 at 1:54 1 good critique! It is not meant to be directly inherited by user-defined classes (for that, use Exception). –stephenbez Aug 28 '12 at 20:44 3 Also the answers to this post point out