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Summary

This Python module does not know how to play chess, but does understand the rules enough that it can watch moves and verify that they are correct.

Getting the software

The software is available in a tarball here: "http://www.alcyone.com/pyos/chess/chess-latest.tar.gz", http://www.alcyone.com/pyos/chess/chess-latest.tar.gz.

The official URL for this Web site is "http://www.alcyone.com/pyos/chess/", http://www.alcyone.com/pyos/chess/.

Features

This module has the following features:

• high abstraction
• understands various notations, including algebraic, long algebraic, and standard algebraic notation (as in PGN); does disambiguation
• supports saving and loading of the state of a game
• not a trivial move processor; understands the intracies of the game

Basics

The following standard abbreviations are used:

• K = king
• Q = queen
• B = bishop
• N = knight (note: not Kn)
• R = rook
• P = pawn

Uppercase letters are used to represent white pieces, lowercase black. Squares on the chessboard are identified with the standard algebraic notation of a (lowercase) letter a-h followed by a number 1-8, which represent file (column) and rank (row) respectively, with 1 being the white home rank and 8 being black. The default state of the chessboard is::

        . . a b c d e f g h . .
        . +-----------------+ .
        8 | r n b q k b n r | 8
        7 | p p p p p p p p | 7
        6 | . . . . . . . . | 6
        5 | . . . . . . . . | 5
        4 | . . . . . . . . | 4
        3 | . . . . . . . . | 3
        2 | P P P P P P P P | 2
        1 | R N B Q K B N R | 1
        . +-----------------+ .
        . . a b c d e f g h . .

Usage

The chest.py test program demonstrates the general way the module is intended to be used. The constants 'WHITE' and 'BLACK' are used to indicate colors. Create a 'Game' instance, call its 'move' method with names, which returns instances of a 'Move' class to indicate the state of the resulting move, and raises errors on encountering problems. The 'ok' method indicates whether or not the game is over.

Notation

The move disambiguator is somewhat sophisticated and understands a variety of notation types:

**algebraic notation (AN)** -- The most widely used of simple chess notations, simply consisting of two algebraic locations indicating a starting square and an ending square; e.g., d2d4, g1f3, d5e6.

**long algebraic notation (LAN)** -- Extended algebraic, including an intervening *-* for moves and x for piece captures, as well as a preceding (uppercase, regardless of color) piece type; e.g., Pd2-d4, Ng1-f3, Pd5xe6.

**standard algebraic notation (SAN)** -- As described by the Portable Game Notation (PGN). "A full specification is available", http://www.very-best.de/pgn-spec.htm, but the key features are as follows:

• Non-capturing moves generally involve only the piece type and the destination square, where pawns are generally not listed; e.g., d4, Nf3, Qd6. When disambiguation of moves is necessary, the file of the desired piece should be indicated; e.g., Nce2, Raf1.
• Captures are indicated with by putting an x between the piece type and the destination square; for pawns, the file of the capturing piece is used; e.g., fxg6, Qxa5. When further disambiguation is necessary, full algebraic notation may be used; e.g., Qc3xa5.
• Kingside castle is indicated with O-O, queenside with O-O-O.
• A suffixed *+* indicates check, a suffixed *#* indicates checkmate.
• A *=* followed by a piece name indicates pawn promotion (pawn promotion indicator comes before check or checkmate indicator, if appropriate).

**hybrids** -- The disambiguator understands (obvious) hybrids as well; e.g., Pxg6.

Known problems

• Engine written entirely in Python and not designed for speed.
• Game does not detect stalemate.
• Castling and pawn promotion implementations are a little weird; they require stowing away data in attributes inside the pieces.

Wish list

• A barely competent computer-controlled chess player would be nice.
• It would be nice if the system truly understood complete PGN games, with all game notations.
• A chess game browser would be nice, where a full game could be loaded and navigated.
• It would be good if more game formats were understood, e.g., Forsyth-Edwards notation, etc.
• Interaction with xboard would be swell.
• Support for such notations as PxP (pawn takes pawn), as well as other somewhat more traditional notations would be nice.
• This was chiefly written before I had upgraded to 2.0, so some 1.5-isms are around.

License

This code is released under the "GPL", http://www.gnu.org/copyleft/gpl.html. If you use this software, "I'd like to know about it", mailto:pyos@alcyone.com.

Release history

• 1.0.2; 2002 Feb 24. Bug with en passant moves fixed.
• 1.0.1; 2002 Feb 2. Include GPL license document, minor text changes.
• 1.0; 2001 May 19. Initial release.

Author

This module was written by "Erik Max Francis", http://www.alcyone.com/max/, who, curiously enough, is not a very strong chess player.

Version

Version 1.0.2a $Date: 2002/07/25 $ $Author: max $