--- a/python/cvutils.py	Tue Mar 24 14:17:12 2015 +0100
+++ b/python/cvutils.py	Tue Mar 24 18:11:28 2015 +0100
@@ -95,7 +95,7 @@
 
     def cvPlot(img, positions, color, lastCoordinate = None):
         last = lastCoordinate+1
-        if lastCoordinate != None and lastCoordinate >=0:
+        if lastCoordinate is not None and lastCoordinate >=0:
             last = min(positions.length()-1, lastCoordinate)
         for i in range(0, last-1):
             cv2.line(img, positions[i].asint().astuple(), positions[i+1].asint().astuple(), color)
@@ -140,7 +140,7 @@
                     if printFrames:
                         print('frame {0}'.format(frameNum))
                     frameNum+=1
-                    if text != None:
+                    if text is not None:
                        cv2.putText(img, text, (10,50), cv2.cv.CV_FONT_HERSHEY_PLAIN, 1, cvRed) 
                     cvImshow(windowName, img, rescale)
                     key = cv2.waitKey(wait)
@@ -234,7 +234,7 @@
             ret = True
             frameNum = firstFrameNum
             capture.set(cv2.cv.CV_CAP_PROP_POS_FRAMES, firstFrameNum)
-            if lastFrameNumArg == None:
+            if lastFrameNumArg is None:
                 from sys import maxint
                 lastFrameNum = maxint
             else:
@@ -250,7 +250,7 @@
                     for obj in objects:
                         if obj.existsAtInstant(frameNum):
                             if not hasattr(obj, 'projectedPositions'):
-                                if homography != None:
+                                if homography is not None:
                                     obj.projectedPositions = obj.positions.project(homography)
                                 else:
                                     obj.projectedPositions = obj.positions
@@ -422,7 +422,7 @@
     if points.shape[0] != 2:
         raise Exception('points of dimension {0} {1}'.format(points.shape[0], points.shape[1]))
 
-    if (homography!=None) and homography.size>0:
+    if (homography is not None) and homography.size>0:
         augmentedPoints = append(points,[[1]*points.shape[1]], 0)
         prod = dot(homography, augmentedPoints)
         return prod[0:2]/prod[2]