def add_walls(self):
for x in range(self.width):<EOL><INDENT>self.add_thing(Wall(), (x, <NUM_LIT:0>))<EOL>self.add_thing(Wall(), (x, self.height-<NUM_LIT:1>))<EOL><DEDENT>for y in range(self.height):<EOL><INDENT>self.add_thing(Wall(), (<NUM_LIT:0>, y))<EOL>self.add_thing(Wall(), (self.width-<NUM_LIT:1>, y))<EOL><DEDENT>
Put walls around the entire perimeter of the grid.