In this section, we will animate the fleet so that it has perpetual movement from right to left and vice versa, as shown by the arrows in the following screenshot:

In order to do this, we will learn how to concatenate one animation just after another one is completed. Indeed, we will create an infinite loop of animations so that the fleet is in perpetual movement.

The following code, fragment 1 (of 2), of fleet.py shows how to concatenate these events:

155. # File name: fleet.py (Fragment 1)
156. from kivy.uix.gridlayout import GridLayout
157. from kivy.properties import ListProperty
158. from kivy.animation import Animation
159. from kivy.clock import Clock
160. from kivy.core.window import Window
161. from random import randint, random
162. from dock import Dock
163. 
164. class Fleet(GridLayout):
165.   survivors = ListProperty(())
166. 
167.   def __init__(self,  **kwargs):
168....