def monster_movement(world, player, monsters):
  for monster in monsters:
    if monster['alive'] == True:
      dx = monster['x']-player['x']
      dy = monster['y']-player['y']
      targetx = 0
      targety = 0
      if abs(dx) < 5 and abs(dy) < 5:
        if abs(dy) > 0:
          gradient = abs(dx)/abs(dy)
          angle = atan(gradient)/pi*2
          if angle > 0.33:
            if dx < 0: targetx = 1
            else: targetx = -1
          if angle < 0.67:
            if dy < 0: targety = 1
            else: targety = -1
        else:
          if dx < 0: targetx = 1
          else: targetx = -1
        move_monster(world, player, monster, targetx, targety, monsters)