catching exceptions

[jm.suresh@no.spam.gmail.com]

Steven D'Aprano wrote:
> On Sat, 16 Dec 2006 03:54:52 -0800, jm.suresh at no.spam.gmail.com wrote:
>
> > Hi, In the following program, I have a class Test which has a property
> > x. Its setx function gets a string value and converts it into a float
> > and stores into it.
>
> [snip code]
>
> Python isn't Java. Are you sure you need properties?

I do not know Java. But, object.x = value looks much better than
object.set_x(value) . Is there any harm in doing it, provided I have to
do more than just storing the value.

>
>
> > I am looking for a way to call func1's exception handler also.
> > Basically I want to have the class's error handler as the basic text
> > based one, and in the calling side, If I have gui, I will pop-up a
> > window and say the error message.
> > One solution is to remove the exception handling inside the class and
> > leave the entire thing to the caller (software people call this
> > client?)  side -- if the caller has access to gui it will use gui or
> > else will print the message. Any other way?
>
> The exception is consumed by the try...except block inside the class,
> so func1 never sees the exception. It might as well not exist.
>
> Generally, you should keep your class as simple as possible. It shouldn't
> try to manage any exception it can't recover from. In your case, the class
> can't recover from a failure of float(strvalue), so it shouldn't consume
> the exception. Two ways of doing that:
>
> def _setx(self, strvalue):
>     self._x = float(strvalue)  # just let the exception propagate
>
> or
>
> def _setx(self, strvalue):
>     try:
>         self._x = float(strvalue)
>     except ValueError:
>         raise SomeError('could not set x attribute to %s' % strvalue)
>
> where SomeError should be either ValueError or possibly some custom
> exception (say, MyClassException).
>
> In either case, the error handling is separate from the object that
> generates the error. And that is as it should be. Now your class can
> remain the same, no matter how the rest of your program handles the
> exception.
>
> By the way, if you want your class to generate warnings, perhaps you
> should investigate the Warnings module:
>
> import warnings
> help(warnings)
I will go through it. Thanks a lot.
> 
> 
> 
> -- 
> Steven.