exit failed script run (python)

Question

I have seen several questions about exiting a script after a task is successfully completed, but is there a way to do the same for a script which has failed? I am writing a testing script which just checks that a camera is functioning correctly. If the first test fails it is more than likely that the following tests will also fail; therefore, I want the first failure to invoke an exit and provide output to screen letting me know that there was an error.

I hope this is enough information; let me know if more details are required to help me.

Thank you!

Answer 1

Are you just looking for the exit() function?

import sys

if 1 < 0:
  print >> sys.stderr, "Something is seriously wrong."
  sys.exit(1)

The (optional) parameter of exit() is the return code the script will return to the shell. Usually values different than 0 signal an error.

Answer 2

You can use sys.exit() to exit. However, if any code higher up catches the SystemExit exception, it won't exit.

Answer 3

You can raise exceptions to identify error conditions. Your top-level code can catch those exceptions and handle them appropriately. You can use sys.exit to exit. E.g., in Python 2.x:

import sys

class CameraInitializationError(StandardError):
    pass

def camera_test_1():
    pass

def camera_test_2():
    raise CameraInitializationError('Failed to initialize camera')

if __name__ == '__main__':
    try:
        camera_test_1()
        camera_test_2()
        print 'Camera successfully initialized'
    except CameraInitializationError, e:
        print >>sys.stderr, 'ERROR: %s' % e
        sys.exit(1)

Answer 4

You want to check the return code from the c++ program you are running, and exit if it indicates failure. In the code below, /bin/false and /bin/true are programs that exit with error and success codes, respectively. Replace them with your own program.

import os
import sys

status = os.system('/bin/true')
if status != 0:
    # Failure occurred, exit.
    print 'true returned error'
    sys.exit(1)

status = os.system('/bin/false')
if status != 0:
    # Failure occurred, exit.
    print 'false returned error'
    sys.exit(1)

This assumes that the program you're running exits with zero on success, nonzero on failure.