Fix Python 3 compatibility.

main.py

@@ -1,11 +1,17 @@
+from __future__ import division
+
 from pyglet.gl import *
 from pyglet.window import key
+import sys
 import math
 import random
 import time
 
 SECTOR_SIZE = 16
 
+if sys.version_info[0] >= 3:
+    xrange = range
+
 def cube_vertices(x, y, z, n):
     return [
         x-n,y+n,z-n, x-n,y+n,z+n, x+n,y+n,z+n, x+n,y+n,z-n, # top
@@ -63,7 +69,7 @@ def normalize(position):
 
 def sectorize(position):
     x, y, z = normalize(position)
-    x, y, z = x / SECTOR_SIZE, y / SECTOR_SIZE, z / SECTOR_SIZE
+    x, y, z = x // SECTOR_SIZE, y // SECTOR_SIZE, z // SECTOR_SIZE
     return (x, 0, z)
 
 class Model(object):
@@ -399,7 +405,7 @@ def on_resize(self, width, height):
         # reticle
         if self.reticle:
             self.reticle.delete()
-        x, y = self.width / 2, self.height / 2
+        x, y = self.width // 2, self.height // 2
         n = 10
         self.reticle = pyglet.graphics.vertex_list(4,
             ('v2i', (x - n, y, x + n, y, x, y - n, x, y + n))