Fixed shebangs, added error checking

samples/python2/video.py

@@ -1,4 +1,4 @@
-#/usr/bin/env python
+#!/usr/bin/env python
 
 '''
 Video capture sample.
@@ -30,9 +30,14 @@ Keys:
 '''
 
 import numpy as np
-import cv2
-from time import clock
 from numpy import pi, sin, cos
+
+import cv2
+
+# built-in modules
+from time import clock
+
+# local modules
 import common
 
 class VideoSynthBase(object):