check inputs

netem.py

@@ -28,11 +28,19 @@ parser.add_argument('-L', '--loss',
 
 args = parser.parse_args()
 
+if args.device is None:
+    print STDERR, 'You must specify a device with --device.'
+    exit 1
+if args.namespace is None:
+    print STDERR, 'You must specify a network namespace with --namespace.'
+    exit 1
+
 # Enable network emulation on the device.
 cmd = ["sudo", "/sbin/ip",
        "netns", "exec", args.namespace,
        "tc", "qdisc", "change", "dev", args.device, "root",
        "netem"]
+
 if args.delay is not None:
     cmd.append("delay")
     cmd.append(str(args.delay))