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Python Base Error Class


I'm also fuzzily aware that Exception has some magic parameter args, but I've never known how to use it. And because if the deprecation, you then need both, or you get an error. 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) >>> If all you want is an informative message when your exception is raised, do this: class MyException(Exception): pass raise MyException("My hovercraft is full of eels") That will give a traceback ending Check This Out

share|improve this answer edited Jun 13 '14 at 23:39 Jim Ferrans 17.7k74167 answered Apr 22 '12 at 18:18 frnknstn 2,3321912 4 It looks like you shouldn't inherit from base exception. Similar criticism to the below, but additionally that's not the way to initialize via super, and you'll get a DeprecationWarning if you access the message attribute: Edit: to override something (or The OP doesn't need to do anything tricky, so why write boilerplate to do what the base Exception class already does? –Jeff Bradberry Aug 23 '09 at 22:10 3 ty 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 https://docs.python.org/2/library/exceptions.html

Python Exception Message

python exception share|improve this question edited Jun 5 '12 at 20:37 Eitan T 27.9k113978 asked Aug 23 '09 at 21:29 Nelson 6,43532027 2 *args (or *foo, or *whatever, all that Good parallels with the talk linked in the comment on the OP's question: stackoverflow.com/questions/1319615/… –Bodhi Apr 9 '15 at 0:16 "That's an interesting constraint that future users may not 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 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.

I was tripped up by the following deprecation warning in Python 2.6.2: >>> class MyError(Exception): ... In any case, you only need the __init__ or __str__ if you do something different from what Exception itself does. def __init__(self, message): ... Python Exception Class Methods You would need to do something like this: try: raise MyException({"message":"My hovercraft is full of animals", "animal":"eels"}) except MyException as e: details = e.args[0] print(details["animal"]) It is still possible to pass

Join them; it only takes a minute: Sign up Proper way to declare custom exceptions in modern Python? That's not a whole lot of extra code you need per class. ;) share|improve this answer answered Aug 23 '09 at 21:58 Lennart Regebro 75k17134202 add a comment| Your Answer What is summer in Spanish? "Estío" vs "verano" Why do you use Bitcoin addresses instead of public keys? https://docs.python.org/3/tutorial/errors.html Nor am I sure it's the right way to do things going forward; a lot of the discussion I found online suggested they were trying to do away with args in

share|improve this answer edited Aug 23 '09 at 22:10 Bastien Léonard 31.3k106181 answered Aug 23 '09 at 21:46 M. Python Errno I'm creating a BI framework and I happen to need a ModelNotLoadedError. It's just deprecated. 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.

Python Custom Exception

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 That means that if your exception is a type of a more specific exception, subclass that exception instead of the generic Exception (and the result will be that you still derive Python Exception Message You application will work fine with using message. Python Valueerror Example Update: two answers have suggested overriding __init__, and __str__/__unicode__/__repr__.

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__. his comment is here 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 The code that handles this exception will, ofc, import it –Alvaro Feb 3 '15 at 19:56 @Alvaro I didn't say it was wrong, it just has the downside of 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 Python Filenotfounderror

  1. Utku ALTINKAYA 1,6821626 add a comment| up vote 4 down vote No, "message" is not forbidden.
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  3. 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
  4. I gather from PEP-352 that attribute did have a special meaning in 2.5 they're trying to deprecate away, so I guess that name (and that one alone) is now forbidden?
  5. But simply calling the message variable something else than message does the trick.
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  9. Is this using Exception.args?

Something about Nintendo and Game Over Screen Baking at a lower temperature than the recipe calls for Help me remember which is which: "humoro" and "humuro" How to flood the entire Then you have to adapt to their usage of variables. Word for making your life circumstances seem much worse than they are Half the pentagon! this contact form except NelsonsExceptions: ...

That's an interesting constraint that future users may not appreciate. Python Attributeerror Object Has No Attribute Browse other questions tagged python exception or ask your own question. asked 7 years ago viewed 235699 times active 1 month ago Blog Stack Overflow Podcast #92 - The Guerilla Guide to Interviewing Linked 1 How to write a custom exception class

Avoid passing a dict as a positional argument, future users of your code will thank you.

The default str() and repr() methods in Exception seem to do a good job of printing out any arguments passed into the MyException() constructor. self.errors = errors That way you could pass dict of error messages to the second param, and get to it later with e.errors It also requires exactly two arguments to be Critique of the top answer Maybe I missed the question, but why not: class MyException(Exception): pass Again, the problem with the above is that in order to catch it, you'll either Python 3 Exceptions By "modern Python" I mean something that will run in Python 2.5 but be 'correct' for the Python 2.6 and Python 3.* way of doing things.

The builtin ones are very nice, and your cooperative inheritance ensures that you use it. But in your case, did you consider ModelNotLoadedError as a type of LookupError? –Aaron Hall Feb 3 '15 at 21:16 1 Thanks! class NastyError(ExceptionTemplate): pass and if you don't like that default tuple-like representation, just add __str__ method to the ExceptionTemplate class, like: # ... http://vealcine.com/python-exception/python-standard-error-class.php 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

But you may want to get rid of the deprecation error, of course. Will change it tomorrow –Alvaro Feb 4 '15 at 1:54 1 good critique! Is it good style in modern Python? That seems like a lot of typing, is it necessary?

See docs.python.org/tutorial/… for more information. –Jeff Bradberry Aug 23 '09 at 21:58 1 Understood, but in addition "args" is a special member name for the Exception type. –Nelson Aug 23 When you create custom Exception classes for your application, many of them do not subclass just from Exception, but from others, like ValueError or similar. python.org/dev/peps/pep-0352 shows what is going on behind the scenes with current Exceptions. Thanks for adding it.

Next number in sequence, understand the 1st mistake to avoid the 2nd more hot questions question feed lang-py about us tour help blog chat data legal privacy policy work here advertising current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list. 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 up vote 595 down vote favorite 158 What's the proper way to declare custom exception classes in modern Python?

How does a jet's throttle actually work? self.message = message ... >>> MyError("foo") _sandbox.py:3: DeprecationWarning: BaseException.message has been deprecated as of Python 2.6 It seems crazy that BaseException has a special meaning for attributes named message. Ugh. All user-defined exceptions should also be derived from this class.

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. 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 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 And in that case you can do the __init__ and __str__ needed there, so you don't have to repeat it for every exception.

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