Hi,
I get the same error in python as Imanflow...

Funny thing is it happens on the 3rd call of get_weight() like so:

def find_ball(scales):

call scales.get_weight() at most 4 TIMES

return indexOfHeavierBall

for i in range(1, 8):
leftPan = [i-1]
rightPan = [i]
w = scales.get_weight(leftPan, rightPan)
print "1"
w = scales.get_weight(leftPan, rightPan)
print "2"
w = scales.get_weight(leftPan, rightPan)
print "3"
w = scales.get_weight(leftPan, rightPan)
print "4"

Any hint on what I'm doing wrong?

I think that at least for python the [[True]] board is supposed to be valid. After all bool is a subclass of int and [[1]] is valid as well. So imho all boards [[x]] with x==1 ==> True should also be true. Apart from my favourite kata so far

Check the first field (the left-most 3x3 subset) it has the numbers (1,2,3,2,3,1,3,1,2) in it. It's suppose to have every number between 1 and 9 in it....

This is cool thinking outside the box!!!