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         self._values = [value]
  40         if normalize:
  41             self._normalized = False
  42             self.normalize()
  43
  44
  45
  46     def normalize(self):
  47         """Checks to see if this cell has only one possible value left.  If
  48         so, sets that as its value and eliminates it from every related cell.
  49         This method is exhaustive; that repeated calls should have no effect.
  50         """
  51
  52         if self._normalized:
  53             # Already done
  54             return
  55
  56         # Set this now just in case of infinite looping
  57         self._normalized = True
  58
  59         if not self.solved:
  60             # Don't know the value yet
  61             return
  62
  63         # Elimination time
  64         for constraint in self.constraints:
  65             for cell in constraint.cells:
  66                 if cell == self:
  67                     continue
  68                 cell.eliminate(self.value)
  69
  70
  71     def eliminate(self, value):
  72         """Eliminates the given value as a possibility for this cell."""
  73         if value in self._values:
  74             self._values.remove(value)
  75
  76             if len(self._values) == 0:
  77                 # XXX give me a real exception here
  78                 raise Exception
  79
  80             self._normalized = False
  81             self.normalize()