catch exception in python script which calls another script

Question

I am running python script from another python file. is there a way I can know if an eception occurred in the second script?

EX: script1.py calls script2.py python script2. py -arguments How can script1 know if an exception occurred in script2?

run.py

import subprocess

subprocess.call("python test.py -t hi", shell=True)

test.py

import argparse
print "testing exception"

parser = argparse.ArgumentParser(description='parser')
parser.add_argument('-t', "--test")

args = parser.parse_args()

print args.test
raise Exception("this is an exception")

Thanks

Oleg Pryadko · Accepted Answer · 2015-07-15 02:33:18Z

6

When a Python program throws an Exception, the process returns a non-zero return code. Subprocess functions like call will return the return code by default. So, to check if an exception occurred, check for a non-zero exit code.

Here is an example of checking the return code:

    retcode = subprocess.call("python test.py", shell=True)
    if retcode == 0:
        pass  # No exception, all is good!
    else:
        print("An exception happened!")

Another method would be to use subprocess.check_call, which throws a subprocess.CalledProcessError exception on a non-zero exit status. An example:

try:
    subprocess.check_call(["python test.py"], shell=True)
except subprocess.CalledProcessError as e:
    print("An exception occured!!")

If you need to know which exception occurred in your test program, you can change the exception using exit(). For example, in your test.py:

try:
    pass  # all of your test.py code goes here
except ValueError as e:
    exit(3)
except TypeError as e:
    exit(4)

And in your parent program:

retcode = subprocess.call("python test.py", shell=True)
if retcode == 0:
    pass  # No exception, all is good!
elif retcode == 3:
    pass  # ValueError occurred
elif retcode == 4:
    pass  # TypeError occurred
else:
    pass  # some other exception occurred

edited Jul 15, 2015 at 2:33

answered Jul 21, 2014 at 3:32

Oleg Pryadko

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1 Comment

Oleg Pryadko Over a year ago

@user3330263 updated answer to reflect your example code

tsbertalan · Accepted Answer · 2014-07-21 03:32:06Z

0

Probably the best method is to make script2 an actual module, import what you want from it into script1, then use the existing try/except mechanic. But perhaps that's not an option? Otherwise I think what gets returned from os.system would probably include what you need.

answered Jul 21, 2014 at 3:32

tsbertalan

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catch exception in python script which calls another script

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