Don't you want to win a free book?

 At the end of Day 2 of the contest, still only one entry. If this keeps up, by next Monday there will not be a draw for a prize, and we will have a winner by default.

The submission was based on the use of __slots__. In playing around with similar cases, I found an AttributeError message that I had not seen before.  Here's a sample code.

class F:
    __slots__ = ["a"]
    b = 1

f = F()
f.b = 2

What happens if I execute this code using Friendly-traceback. Normally, there would be an explanation provided below the list of variables. Here we see nothing.

Let's inspect by using the friendly console.

I'll have to take care of this later today. Perhaps you know of other error messages specific to the use of __slots__. If so, and if you are quick enough, you could enter the contest. ;-)