new_contents: from ggame import App, RectangleAsset, ImageAsset, Sprite, LineStyle, Color, Frame
  
  class Bullet(Sprite):
      asset = ImageAsset("images/300px-BM_Grenade.png", Frame(100,20,100,115), 1, 'vertical')
  
      def __init__(self, position):
          super().__init__(Bullet.asset, position)
          self.vx=1
          self.vy=-.5
          self.vr=1
          self.scale=.5
          self.vr=0
          self.fxcenter = .5
          self.fycenter = .5
  
      def step(self):
          self.x += self.vx
          self.y += self.vy
          self.vy += .05
          self.rotation += .1
  
subject: Create bullet.py