John Gordon wrote:
I'm trying to come up with a scheme for organizing exceptions in
my application.
Currently, I'm using a base class which knows how to look up the text
of a specific error in a database table, keyed on the error class name.
The base class looks like this:
class ApplicationException(Exception):
"""Base class for application-specific errors."""
def get_message(self):
"""Return the error message associated with this class name."""
class_name = self.__class__.__name__
return UserMessage.objects.get(key=class_name).text
And then I define a bunch of subclasses which all have different names:
class QuestionTooShortError(NetIDAppsError):
"""User entered a security question which is too short."""
pass
class QuestionTooLongError(NetIDAppsError):
"""User entered a security question which is too long."""
pass
This scheme works, but I'd like to make it more streamlined. Specifically,
I'd like to group the classes underneath a parent class, like so:
class Question(ApplicationException):
class TooShort(ApplicationException):
pass
class TooLong(ApplicationException):
pass
This will make it easier in the future for organizing lots of sub-errors.
My problem is this: the get_message() method in the base class only knows
the current class name, i.e. "TooShort" or "TooLong". But that's not
enough; I also need to know the outer class name, i.e. "Question.TooShort"
or "Question.TooLong". How do I get the outer class name?
Thanks,
You're going way too much into details regarding your exceptions.
Basically, you need to create an exception class is at some point you
need different handlers.
For instance,
try:
whatever()
except Question.TooShort:
dosomething()
except Question.TooLong:
dosomethingelse()
But I'm not sure you really need this.
Try to keep it simple.
You fetch you exception message from a database, is that really required
? Why can't you just write it in your code ?
Another problem is getting the database key from the class name, this
makes difficult changing any class name, I'm not sure this is a good idea.
Anyway I'm not sure I'm helping here, providing more questions than answer.
What you could do :
class AppException(Exception): pass
class Question(AppException): pass
class TooShort(Question): pass
class TooLong(Question): pass
def getName(cls):
if not hasattr(cls, '__base__'):
raise ValueError('Not a new class style')
if cls is AppException:
return cls.__name__
return getName(cls.__base__)+'.' + cls.__name__
> getName(TooShort)
< 'AppException.Question.TooShort'
This implies you're using only inheritance, not using class as
ccontainer/namespace.
JM
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