code: def get_angle_difference(v1, v2):
      
      v1 = numpy.array(v1)
      v2 = numpy.array(v2)
      angle=numpy.arccos(old_div((numpy.dot(v1, v2) ), (numpy.sqrt(math.fsum(v1**2)) * numpy.sqrt(math.fsum(v2**2)))))    
      return math.degrees(angle)
docs: returns angular difference in degrees between two vectors.  takes in cartesian coordinates.