old_contents: # Use x, y coords for unit positions
  # (97, 56) ... (104, 56)
  #    ...          ...
  # (97, 49) ... (104, 49)
  #
  # Algebraic notation for a position is:
  # algebraic_pos = chr(x) + chr(y)
  
  
  def _coord_to_algebraic(coord):
      x, y = coord
      return chr(x) + chr(y)
  
  
  def _algebraic_to_coord(algebraic):
      x, y = algebraic[0], algebraic[1]
      return ord(x), ord(y)
  
  
  def _is_pos_on_board(coord):
      u"""Return True if coordinate is on the board."""
      x, y = coord
      if (97 <= x <= 104) and (49 <= y <= 56):
          return True
      else:
          return False
  
new_contents: # Use x, y coords for unit positions
  # (97, 56) ... (104, 56)
  #    ...          ...
  # (97, 49) ... (104, 49)
  #
  # Algebraic notation for a position is:
  # algebraic_pos = chr(x) + chr(y)
  
  
  def _coord_to_algebraic(coord):
      x, y = coord
      return chr(x) + chr(y)
  
  
  def _algebraic_to_coord(algebraic):
      x, y = algebraic[0], algebraic[1]
      return ord(x), ord(y)
  
  
  def _is_pos_on_board(coord):
      u"""Return True if coordinate is on the board."""
      x, y = coord
      if (97 <= x <= 104) and (49 <= y <= 56):
          return True
      else:
          return False
  
  
  class Piece(object):
      """Parent class for chess pieces."""
      def __init__(self, pos):
          """Instantiate a piece at a coordinate position."""
          super(Piece, self).__init__()
          if isinstance(pos, str):
              self.x, self.y = _algebraic_to_coord(pos)
          else:
              self.x, self.y = pos
  
subject: Add Piece() to serve as the parent class for all chess pieces