Capturing errors raised by other scripts ?
lie.1296 at gmail.com
Sat Feb 20 09:04:22 CET 2010
On 02/20/10 14:39, northof40 wrote:
> 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
>>> class customError(Exception):
>>> def __init__(self, value):
>>> self.value = value
>>> def __str__(self):
>>> return repr(self.value)
>>> 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-')
>>> ... 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".
Not really; not all that is written to stderr signifies errors per se.
Warning and Debugging info are often written to stderr as well.
> 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.
Tracebacks is almost always written to stderr, not stdout; unless the
programmer explicitly redirect the traceback into stdout.
> 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 ?).
A well-behaved program will exit with status code 0; if and only if it
exited cleanly. I believe a python program that exited due to unhandled
exception always return non-zero status code.
However, if the program handled an error and called exit(0) explicitly
or the execution of the program falls to the end of the module; there is
no way to distinguish it from regular clean exit.
More information about the Python-list