Print stuff in backtracking module only; clean up the \r stuff

sudoku/__init__.py

@@ -162,7 +162,6 @@ class Sudoku:
         if idx in self._clues:
             raise SquareIsClue('Cannot set clue square ({},{})'.format(x, y))
         self._board[idx] = value
-        print('({},{}) <- {} {!r}'.format(x, y, value, self))
 
     def _xy_to_idx(self, x, y):
         return y * self.row_size + x

sudoku/solvers/backtracker.py

@@ -26,8 +26,10 @@ def _solve_square(sudoku, x, y):
             continue
         except NoPossibleValues:
             # Need to backtrack.
-            sudoku.unset(x, y)
-            raise Backtrack()
+            should_backtrack = True
+            break
+
+        print('\r{!r}'.format(sudoku), end='', flush=True)
 
         next_coord = _next_coord(sudoku, x, y)
         if not next_coord:
@@ -40,13 +42,14 @@ def _solve_square(sudoku, x, y):
             continue
 
     if should_backtrack:
-        # Unhandled backtrack. Pop out of this one too.
         try:
             sudoku.unset(x, y)
         except SquareIsClue:
             pass
         raise Backtrack()
 
+    print()
+
     return sudoku
 
 def _next_coord(sudoku, x, y):