"""drop the entire fleet and change the fleet' direction ""for alien in aliens sprites() alien rect +ai_settings fleet_drop_speed ai_settings fleet_direction *- def update_aliens(ai_settingsaliens)""check if the fleet is at an edgeand then update the postions of all aliens in the fleet "" check_fleet_edges(ai_settingsaliensaliens update(in check_fleet_edges()we loop through the fleet and call check_edges(on each alien if check_edges(returns truewe know an alien is at an edge and the whole fleet needs to change directionso we call change_fleet_direction(and break out of the loop in change_fleet_direction()we loop through all the aliens and drop each one using the setting fleet_drop_speed vthen we change the value of fleet_direction by multiplying its current value by - we've modified the function update_aliens(to determine whether any aliens are at an edge by calling check_fleet_edges( this function needs an ai_settings parameterso we include an argument for ai_settings in the call to update_aliens()alien_ invasion py start the main loop for the game while truegf check_events(ai_settingsscreenshipbulletsship update(gf update_bullets(bulletsgf update_aliens(ai_settingsaliensgf update_screen(ai_settingsscreenshipaliensbulletsif you run the game nowthe fleet should move back and forth between the edges of the screen and drop down every time it hits an edge now we can begin shooting down aliens and watch for any aliens that hit the ship or reach the bottom of the screen try it yourse lf - raindropsfind an image of raindrop and create grid of raindrops make the raindrops fall toward the bottom of the screen until they disappear - steady rainmodify your code in exercise - so that when row of raindrops disappears off the bottom of the screena new row appears at the top of the screen and begins to fall aliens