Test if a file exists and is not group-writable

test_not_group_write.py

#!/usr/bin/python
"""Test if a file exists and is not group-writable.

AUTHOR: joe.ashcraft@rackspace.com
"""

from __future__ import print_function
import os, stat, sys


def usage():
    print("FATAL: invalid usage", file=sys.stderr)
    print("USAGE:  %s  file" % __file__)
    sys.exit(1)


def file_not_found():
    print("file not found", file=sys.stderr)
    sys.exit(1)


def result_bad(n=999):
    print("file is group writable")
    sys.exit(n)


def result_good():
    print("file is not group writable")
    sys.exit(0)


try:
    FILE = os.path.expanduser(sys.argv[1])
except IndexError:
    usage()

if not os.path.exists(FILE):
    file_not_found()

# bitwise AND to test if the group-writable bit is set
result = os.stat(FILE).st_mode & stat.S_IWGRP

if result != 0:
    result_bad(result)
else:
    result_good()