Capturing errors raised by other scripts ?

northof40 shearichard at gmail.com
Sat Feb 20 04:39:23 CET 2010


On Feb 20, 4:13 pm, MRAB <pyt... at mrabarnett.plus.com> wrote:
> northof40 wrote:
> > I'm using the subroutine module to run run python script A.py from
> > B.py (this is on windows fwiw).
>
> > A.py is not my script and it may raise arbitary errors before exiting.
> > How can I determine what's happened before A.py exited ?
>
> > To simulate this I've got this script (which is meant to simulate
> > A.py):
>
> > class customError(Exception):
> >    def __init__(self, value):
> >            self.value = value
> >    def __str__(self):
> >            return repr(self.value)
>
> > try:
> >    raise customError(2*2)
> > except customError as e:
> >    print 'Custom exception occurred, value:', e.value
>
> > I then run my A.py like this :
>
> >>>> fdOut, fOut = tempfile.mkstemp(suffix='.txt', prefix='AOut-')
> >>>> fdErr, fErr = tempfile.mkstemp(suffix='.txt', prefix='AErr-')
> >>>> try:
> > ...     pathtojob="python.exe A.py"
> > ...     p = subprocess.Popen(pathtojob, stderr=fdErr, stdout=fdOut)
> > ... except:
> > ...     print "bad stuff happened"
> > ...
>
> > When I do this I the exception handler is not fired and the text
> > "Custom exception occurred, value: 4" ends up in the stdout file.
>
> > I'd really like it to end up in stderr because then I could say
> > "anything in stderr ? then ignore the output and flag an error".
>
> > I don't want to have to parse the stdout for error like messages and I
> > can't make changes to A.py.
>
> > I'm sure there's a better way to do this - can anyone offer some
> > advice ?
>
> > thanks
>
> A.py is printing the error message.
>
> The 'print' statement prints to stdout unless you direct it elsewhere
> with '>>', for example:
>
>      print >> my_file, 'message'
>
> If you don't want error messages to go to stdout, then don't print them
> to stdout, it's as simple as that!

Thanks for your reply. I take your point about print - perhaps I
hadn't really thought that through. Unfortunately I don't have control
of the real script that's being run so if the programmer of that
script has used print there's nothing I can do about it.

Perhaps I could modify the question. If A.py terminates due an
unhandled exception is there anyway for B.py to know that's happened
(without A.py's cooperation ?).

thanks

Richard.


If A.py terminates due to an unhandled exception



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