How do you attract a lost pet snake out of hiding?

If the snake isn't coming out that likely means it is both full and comfortable. Start by dropping the temperature in the room it is in several degrees while simultaneously putting a warm spot out that will attract its attention. You can accomplish this by setting a lamp in the middle of the floor and turning it on. Try doing this at night and then sit quietly and wait to see if the snake comes out. It might take a few hours before it starts to move if it does at all.

Another method is to get a frozen rat/mouse, thaw it out and set it in the middle of the floor in a container of some sort. If the snake is in the room, even if it just ate there's a pretty good chance it will come out to investigate. Of course like the above method you need to be there to see it come out and catch it.

If you don't know for sure where it is, but only suspect you can try laying flour out along the edges of the wall. The theory is that the snake will crawl through it and confirm by way of its body impressions in the flour that it is in that room.