Without seeing the input it's hard to tell...

Hey, I got an error in my final submission:

It should work for random inputs too:
'-63,-61--59,-56,-55,-53,-50,-47,-45,-43,-41,-40,-38,-35,-33--28,-26,-25,-23,-22,-20' should equal
'-63,-61--59,-56,-55,-53,-50,-47,-45,-43,-41,-40,-38,-35,-33--28,-26,-25,-23,-22,-20,-18,-15'

Where'd I get the two last items?

Very nice kata, I had a good time solving it. :)

I think you're inflicting some unnecessary sufferring with this line:

str(a) == '(1,2,3)'

The default tuple for python has spaces after the ,. So it would be (1, 2, 3).

It's the difference of using the built in tuple() function and writing it out.