tiwo / exactcover Goto Github PK

The code now builds under both Python2 and Python3, and I can't see any complications. Unter Python 2.7, the examples/sudoku.py dutifully prints a solution and its "partition". Yet under Python 3 (3.4 as well as "nightly" on travis), it behaves differently, doesn't find a solution, and raises Stopiteration in solution = exactcover.Coverings(m).next().

Under Python 2.7, the for(;;)-loop in Coverings_next(self) runs exactly 81 times without ever backtracking before it finds the solution.* Under Python 3, that loop runs once, calls Coverings_step(self); which returns CONTINUE. In the next, second, loop iteration, Coverings_step(self); already returns BACKUP and Coverings_backup(self) returns -1 which causes l. 448 to return NULL. Why?

(* Btw, why exactly 81 iterations? Why not less when some numbers are given? Why no backtracking step?)