9 

    10 class CommandError(Exception): pass

    11 

    12 def explain_exit(code):

    13     """return a 2-tuple (desc, code) describing a process's status"""

    14     if os.WIFEXITED(code):

    15         val = os.WEXITSTATUS(code)

    16         return "exited with status %d" % val, val

    17     elif os.WIFSIGNALED(code):

    18         val = os.WTERMSIG(code)

    19         return "killed by signal %d" % val, val

    20     elif os.WIFSTOPPED(code):

    21         val = os.STOPSIG(code)

    22         return "stopped by signal %d" % val, val

    23     raise ValueError("invalid exit code")

    24     

    25 def system(cmd, errprefix = "abort"):

    26     """execute a shell command that must succeed"""

    27     rc = os.system(cmd)

    28     if rc:

    29         errmsg = "%s: %s %s" % (errprefix, os.path.basename(cmd.split(None, 1)[0]),

    30                                 explain_exit(rc)[0])

    31         raise CommandError(errmsg)