code: def url(self, service):
  		'''return URL for a tile'''
  		if service not in TILE_SERVICES:
  			raise TileException('unknown tile service %s' % service)
  		url = string.Template(TILE_SERVICES[service])
  		(x,y) = self.tile
  		tile_info = TileServiceInfo(x, y, self.zoom)
  		return url.substitute(tile_infof url(self, service):
  		'''return URL for a tile'''
  		if service not in TILE_SERVICES:
  			raise TileException('unknown tile service %s' % service)
  		url = string.Template(TILE_SERVICES[service])
  		(x,y) = self.tile
  		tile_info = TileServiceInfo(x, y, self.zoom)
  		return url.substitute(tile_info)
docs: return URL for a tile