Answers

Exercise A:

normalize(Quaternion q)
  length = sqrt( pow(w,2) + pow(x,2) + pow(y,2) + pow(z,2))
  q.w /= length
  q.x /= length
  q.y /= length
  q.z /= length

Exercise B:

def rotate_with_mouse(self, yaw, pitch):
    right = pygame.Vector3(1, 0, 0)
    up = pygame.Vector3(1, 0, 0)
    y_rot = Quaternion(axis=up, angle=self.mouse_invert * yaw * 
                       self.mouse_sensitivityY)
    x_rot = Quaternion(axis=right, 
                       angle=self.mouse_invert * pitch * 
                       self.mouse_sensitivityX)
    m_rot = x_rot * y_rot
    self.transform...