[Tutor] How to raise error without the stack trace

[Rich Lovely]

On 26 November 2011 11:41, Steven D'Aprano <steve at pearwood.info> wrote:
> Hugo Arts wrote:
>>
>> On Sat, Nov 26, 2011 at 11:16 AM, Karim <kliateni at gmail.com> wrote:
>>>
>>> Hello,
>>>
>>> I want to fire my own exception without having the (useful but ugly in my
>>> case) stack trace display.
>>>
>>> How to modify a Exception type class for that purpose which looks like:
>>>
>>> classs MyError(Exception):
>>>      pass
>>>
>>> Cheers
>>> Karim
>>>
>>
>> The stack trace is what happens when an exception is uncaught. You
>> don't need to modify it. What you want to do is catch the exception,
>> print it, then, depending on whether you can recover from the error,
>> possibly do a sys.exit(-1).
>
> If you can recover from the error, by all means catch the exception. That's
> what exceptions are for!
>
> But otherwise, please think very, very, VERY carefully before printing an
> error message and exiting. This is normally the wrong thing to do.
>
> Stack traces are useful. They show you exactly what has gone wrong, and
> where (although sadly not why!). There is very little worse than a "helpful"
> programmer who turns a sensible, useful stack trace into a useless, stupid
> message:
>
> "An error has occurred"
>
> or worse.
>
> Perhaps the most sensible example I can think of is this:
>
>
> def main():
>    # your code goes here...
>
>
> if __name__ == '__main__':
>    try:
>        main()
>    except KeyboardInterupt:
>        # Not an error, so no need for a stack trace.
>        print "operation cancelled by user"
>        sys.exit(1)
>
>
> and that's it. Any other exception is a bug in your code, and so the stack
> trace should be printed so the user can report it.
>
>
> --
> Steven
>
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Although there's nothing wrong with taking the stack trace and
cleaning it up - perhaps dumping it to a logfile, using the Traceback
module.  Asking your users to send a file (or even automating the
process in your except: block is much more user friendly than
expecting them to be able to copy and paste from a (potentially
hidden, for GUI apps) console.  It also ensures you get the entire
stack trace, rather than just what they think is useful.

-- 
Rich "Roadie Rich" Lovely

Just because you CAN do something, doesn't necessarily mean you SHOULD.
In fact, more often than not, you probably SHOULDN'T.  Especially if I
suggested it.

10 re-discover BASIC
20 ???
30 PRINT "Profit"
40 GOTO 10