Bug: Fixing (mostly) snatch

Now keeping the memory diagram open in another window, or perhaps at your side in print form, let's consider the bug identified in the original Bat.snatch method. The code is this,

This seems sensible. Remember that self is a Bat, so the line says to change self's location attribute to a random room number. There is nothing wrong with this as far as it goes, but more needs to be done. Look at Room 12 in the diagram which contains a Bat. Suppose the Bat's new location is Room 8. If we only change the Bat's location attribute to be 8 then Room 12 will still think it has a Bat in it (see the arrow from Room 12's bat attribute?) and Room 8 won't know it now has a Bat in it because we haven't assigned it one. So in addition to changing the Bat's location attribute to 8 we need to change Room 12's bat attribute to None, and Room 8s bat attribute to reference this Bat object.

In visual terms we are starting with this,

and only ending up with this,

but we need to end up with this,

The new code does that,

Another Bug

Another smaller less subtle bug remains. When the bat's new room is chosen it shouldn't be a room with a Bat already in it, nor should it be the room it has just dropped the player in (which will happen approximately 1 in 20 times since we are choosing randomly). Fixing this secondary bug will be part of your assignment.