width the space needed to display one alien is twice its widthone width for the alien and one width for the empty space to its right to find the number of aliens that fit across the screenwe divide the available space by two times the width of an aliennumber_aliens_x available_space_x ( alien_widthwe'll include these calculations when we create the fleet one great aspect about calculations in programming is that you don' have to be sure your formula is correct when you first write it you can try it out and see if it works at worstyou'll have screen that' overcrowded with aliens or has too few aliens you can revise your calculation based on what you see on the screen note creating rows of aliens to create rowfirst create an empty group called aliens in alien_invasion py to hold all of our aliensand then call function in game_functions py to create fleetalien_ invasion py import pygame from pygame sprite import group from settings import settings from ship import ship import game_functions as gf def run_game()--snip-make shipa group of bulletsand group of aliens ship ship(ai_settingsscreenbullets group( aliens group( create the fleet of aliens gf create_fleet(ai_settingsscreenaliensw start the main loop for the game while true--snip-gf update_screen(ai_settingsscreenshipaliensbulletsrun_game(because we're no longer creating aliens directly in alien_invasion pywe don' need to import the alien class into this file create an empty group to hold all of the aliens in the game thencall the new function create_fleet(vwhich we'll write shortlyand pass it the ai_settingsthe screen objectand the empty group aliens nextmodify the call to update_screen(to give it access to the group of aliens