Deriving from Exception

[Fredrik Lundh]

"pixie888 at hotmail.com" wrote:

> I have some classes which derive from Exception, however in the
> __init__ function I do not call the __init__ function of Exception
> itself, allthough I think I should. The reason I don't do it is
> because I see that in all the tutorials about Python the tutors
> themselves don't do it either.
>
> Can anybody tell me why?

The Exception baseclass provides an __init__ method which
takes all arguments and puts them in an args attribute.

It also provides default __str__ and __getitem__ methods,
so you can print the exception, and use the v[x] notation
to access the members.

In Python, the class would look something like this:

class Exception:

    def __init__(self, *args):
        self.args = args

    def __str__(self):
        if not self.args:
            return ''
        elif len(self.args) == 1:
            return str(self.args[0])
        else:
            return str(self.args)

    def __getitem__(self, i):
        return self.args[i]

If this behaviour is fine for your exception subclass, there's
no need to override anything.

</F>