pseudoku/grid/cell.py

   1 from operator import attrgetter
   2 from weakref import ref
   3
   4 class Cell(object):
   5     """Represents a single cell/value within a sudoku grid."""
   6
   7     ### Accessors
   8
   9     def _get_solved(self):
  10         """True iff this cell has been solved."""
  11         return len(self._values) == 1
  12     solved = property(_get_solved)
  13
  14     def _get_value(self):
  15         """Returns this cell's value, if it has one known."""
  16         if self.solved:
  17             return self._values[0]
  18         return None
  19     value = property(_get_value)
  20
  21     grid = property(lambda self: self._grid())
  22     constraints = property(attrgetter('_constraints'))
  23
  24     def __init__(self, grid, row, column):
  25         self._grid = ref(grid)
  26         self._row = row
  27         self._col = column
  28         self._values = range(self.grid.size)
  29         self._constraints = []
  30         self._normalized = False
  31
  32     def add_constraint(self, constraint):
  33         self._constraints.append(constraint)
  34
  35     def set(self, value, normalize=True):
  36         """Sets the value of this cell.  If `normalize` is True or omitted, the
  37         grid will be updated accordingly.
  38
  39         Returns the number of cell changes.
  40         """
  41         self._values = [value]
  42         if normalize:
  43             self._normalized = False
  44             return self.normalize() + 1
  45
  46         return 1
  47
  48
  49     def normalize(self):
  50         """If this cell has been solved, eliminates its value as a candidate
  51         from every other cell in every group it's in.
  52         This method is exhaustive; repeated calls should have no effect.
  53
  54         Returns the number of cell changes.
  55         """
  56
  57         if self._normalized:
  58             # Already done
  59             return 0
  60
  61         # Set this now just in case of infinite looping
  62         self._normalized = True
  63
  64         if not self.solved:
  65             # Don't know the value yet
  66             return 0
  67
  68         # Elimination time
  69         cell_changes = 0
  70         for constraint in self.constraints:
  71             for cell in constraint.cells:
  72                 if cell == self:
  73                     continue
  74                 cell_changes += cell.eliminate(self.value)
  75
  76         return cell_changes
  77
  78     def eliminate(self, value):
  79         """Eliminates the given value as a possibility for this cell.
  80
  81         Returns the number of cell changes."""
  82         if value not in self._values:
  83             return 0
  84
  85         self._values.remove(value)
  86
  87         if len(self._values) == 0:
  88             # XXX give me a real exception here
  89             raise Exception
  90
  91         self._normalized = False
  92         return self.normalize() + 1