"Alien Invasion" Python Game

Each player controls a ship that is located in the middle of the bottom edge of the screen. The player moves the ship to the right and left with the control keys or the cursor; the spacebar is used for shooting. At the beginning of the game, the alien fleet is located at the top of the screen and gradually falls down, also shifting to the side. The player destroys the aliens with shots. If he manages to shoot down all the aliens, a new fleet appears, which moves faster than the previous one. If the alien collides with the player's ship or reaches the bottom edge of the screen, the player loses the ship. If the player loses all three ships, the game ends.