can error messages be improved or can they be overridden ?

Stef Mientki stef.mientki at
Mon Feb 23 19:37:17 CET 2009

rdmurray at wrote:
> Stef Mientki <stef.mientki at> wrote:
>> thanks Ron,
>> but I was looking for a more general solution,
>> in which I don't change the program itself,
>> and where the error messages (in general) become more informative than 
>> it is by default.
> [snip]
>>>> -----Original Message-----
>>>> From: Stef Mientki [mailto:stef.mientki at] 
> [snip]
>>>> I often get an error message like this
>>>>     self.Brick.Par [ self.EP[2] ]['FileName'] = filename
>>>> IndexError: list index out of range
>>>> Now it would be very welcome,
>>>> if the error message specified which index is out of range, 
>>>> in this case e.g.,
>>>> - specifying the length of self.EP
>>>> - specifying the value of self.EP[2]
>>>> - specifying the length of self.Brick.Par etc..
>>>> Is there a way to override the error message and provide this 
>>>> information, or is it impossible ?
>>>> And if it's possible, am I the only one who often stumbles 
>>>> about this problem ?
>>>> (I expect many people must have bounced in this problem before me ;-)
> FYI, top posts are much harder to read and to reply to than if you edit
> the message to which you are replying and add your new content interleaved
> or at the bottom (as I have done).
??? I read that before, but I can't understand it.
I think that depends totally on the mail reader you use (although I 
don't know any mail reader that scrolls to the bottom).
I use Thunderbird, which opens every message at the top,
so top posting is the best readable for me,
I don't have to scroll (assuming that I know from previous readings the 
content of the previous message).
Replying can be preset in any reader I know just as you like, bottom or top.
So I guess there must be another reason, why some (or maybe even 
everyone except me)  don't prefer top posting.
> No you are not the only one who wishes the error messages were
> more informative.  In one complex application I had, I made my life
> easier with a hack I copied from Zope.  Briefly, at the top level
> of the program I trap all exceptions, get the traceback object from
> sys.exc_info, format it with format_tb, and then process it to add info.
> I applied several enhancements, but the one relevant to you was to grab
> the locals dictionary from the last frame of the traceback, and use a
> regex to split the last source line in the formatted traceback up into
> candidate variable names.  Then I printed the name and the repr of the
> value of any of those names I found in the locals dict.
> That wouldn't tell you directly which variable it was threw the index
> error, but having the current values of the variables involved saves a
> lot of time (no need to go back and stick in prints in many cases).
> (You know, I really ought to revisit that routine and make it part
> of my standard development toolbox.)
well that sound good,
but contains a lot of suggestions with which I'm not familiar.
Could please post some code snippets ?

Stef Mientki
> --RDM
> --

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