[wxPython-users] Advice on catching exceptions?

[Robin Dunn]

Marc Hedlund wrote:
> 
> Hi,
> 
> I have a wxPython app which makes extensive use of the python logging 
> package to write out a log file.  For the most part, that works great, 
> but in a few cases, exceptions seem to elude the exception handlers I 
> have set up: (1) in some event handlers that don't have enough exception 
> handling themselves; and (2) when the logging package itself throws an 
> exception. In these cases, on Windows 2000, a dialog appears when the 
> application quits, saying "Errors occurred, see C:\Program 
> Files\<mydir>\<myexe>.exe.txt for more information" (paraphrased).
> 
> My main loop used to look like this:
> 
> if __name__ == '__main__':
>     try:
>         # Main event loop startup.
>         app = MyApp(redirect=False)
>         app.MainLoop()
>     except Exception, detail:
>         if not isinstance(detail, SystemExit):
>             logger = logging.getLogger("myloggername")
>             logger.critical("Last-gasp error handler caught an 
> exception!\n%s",
>                             exc_info=sys.exc_info())
> 
> That usually worked, but like I say, some event handler exceptions 
> seemed to elude the except clause. 

See: 
http://lists.wxwidgets.org/cgi-bin/ezmlm-cgi?11:msp:48315:oadlcbijoffnbmmeppbo


> I just made one change to my code in 
> order to try to prevent this:
> 
>         app = MyApp(redirect=True)
> 
> Later on, after I've used wx.StandardPaths to find a good place for the 
> logfile, I call the following inside my app class:
> 
>         self.RedirectStdio(filename=logpath)
> 
> Although, redirecting output doesn't seem like it would make the except 
> clause any more aggressive or effective -- just that it would cause the 
> App object to do its best to catch stdout/stderr.  What I really want is 
> a more effective except clause.
> 
> I don't have a good reproduction case for the "errors occurred" problem 
> I was seeing before, so I'm wondering if there's anything else I should 
> do in order to catch as many exceptions as possible.  Is using 
> wx.App.OnUnhandledException, wx.App.OnFatalException, or 
> wx.App.OnExceptionInMainLoop advisable?  None of those seem to be 
> documented in the python docs, and I'm not sure whether they're needed 
> or useful in this case.

They are currently not wrapped for Python, and they are for dealing with 
C++ exceptions, not Python exceptions.  Also, IIRC, they are different 
based on whether it is a debug or a release build.

-- 
Robin Dunn
Software Craftsman
http://wxPython.org  Java give you jitters?  Relax with wxPython!