How to use the pyscroll.PyscrollGroup function in pyscroll

# create new data source for pyscroll
        map_data = pyscroll.data.TiledMapData(tmx_data)

        # create new renderer (camera)
        # clamp_camera is used to prevent the map from scrolling past the edge
        self.map_layer = pyscroll.BufferedRenderer(map_data,
                                                   screen.get_size(),
                                                   clamp_camera=True)
        self.map_layer.zoom = 2


        # pyscroll supports layered rendering.  our map has 3 'under' layers
        # layers begin with 0, so the layers are 0, 1, and 2.
        # since we want the sprite to be on top of layer 1, we set the default
        # layer for sprites as 2
        self.group = pyscroll.PyscrollGroup(map_layer=self.map_layer)
        self.hero = Hero()

        # put the hero in the starting position of the map
        self.hero.position = get_starting_position(tmx_data.tilewidth,
                                                   starting_position)

        # add our hero to the group
        self.group.add(self.hero)
        if self.fog_enabled:
            self.group.add(self.fog_of_war)

self.screen = world.screen
        w, h = world.screen.get_size()
        #Create new renderer/camera
        self.map_layer = pyscroll.BufferedRenderer(self.world.level.map_data,
                                                   (w, h),
                                                   clamp_camera=False,
                                                   colorkey=None,
                                                   alpha=True)
        #The player, enemies, items etc. should to be on top of
        #layer named in TMX "decoration behind"
        #Find layer number of the layer named "decoration behind"
        self.render_layer = 0
        for layer_index in range(len(self.world.level.tmx_data.layers)):
            if self.world.level.tmx_data.layers[layer_index].name == "walls":
                self.render_layer = layer_index #content will be drawn on top of walls layer
        self.group = pyscroll.PyscrollGroup(map_layer=self.map_layer,
                                            default_layer=self.render_layer)
        #Players image position is actually camera position
        player_image_position = self.world.appearance[self.world.player].rect
        #Parallax background
        self.star_field = parallaxStarfield.ParallaxStarfield(w, h,
                                                              player_image_position.x,
                                                              player_image_position.y)