Add and use rank/file constants

Author: jacksonthall22

chess/__init__.py

@@ -64,8 +64,28 @@ def piece_name(piece_type: PieceType) -> str:
     "P": "♙", "p": "♟",
 }
 
+File: TypeAlias = int
+FILE_A: File = 0
+FILE_B: File = 1
+FILE_C: File = 2
+FILE_D: File = 3
+FILE_E: File = 4
+FILE_F: File = 5
+FILE_G: File = 6
+FILE_H: File = 7
+FILES = [FILE_A, FILE_B, FILE_C, FILE_D, FILE_E, FILE_F, FILE_G, FILE_H]
 FILE_NAMES = ["a", "b", "c", "d", "e", "f", "g", "h"]
 
+Rank: TypeAlias = int
+RANK_1: Rank = 0
+RANK_2: Rank = 1
+RANK_3: Rank = 2
+RANK_4: Rank = 3
+RANK_5: Rank = 4
+RANK_6: Rank = 5
+RANK_7: Rank = 6
+RANK_8: Rank = 7
+RANKS = [RANK_1, RANK_2, RANK_3, RANK_4, RANK_5, RANK_6, RANK_7, RANK_8]
 RANK_NAMES = ["1", "2", "3", "4", "5", "6", "7", "8"]
 
 STARTING_FEN = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
@@ -251,15 +271,15 @@ def square_name(square: Square) -> str:
     """Gets the name of the square, like ``a3``."""
     return SQUARE_NAMES[square]
 
-def square(file_index: int, rank_index: int) -> Square:
+def square(file_index: File, rank_index: Rank) -> Square:
     """Gets a square number by file and rank index."""
     return rank_index * 8 + file_index
 
-def square_file(square: Square) -> int:
+def square_file(square: Square) -> File:
     """Gets the file index of the square where ``0`` is the a-file."""
     return square & 7
 
-def square_rank(square: Square) -> int:
+def square_rank(square: Square) -> Rank:
     """Gets the rank index of the square where ``0`` is the first rank."""
     return square >> 3
 
@@ -376,24 +396,24 @@ def square_mirror(square: Square) -> Square:
 BB_LIGHT_SQUARES: Bitboard = 0x55aa_55aa_55aa_55aa
 BB_DARK_SQUARES: Bitboard = 0xaa55_aa55_aa55_aa55
 
-BB_FILE_A: Bitboard = 0x0101_0101_0101_0101 << 0
-BB_FILE_B: Bitboard = 0x0101_0101_0101_0101 << 1
-BB_FILE_C: Bitboard = 0x0101_0101_0101_0101 << 2
-BB_FILE_D: Bitboard = 0x0101_0101_0101_0101 << 3
-BB_FILE_E: Bitboard = 0x0101_0101_0101_0101 << 4
-BB_FILE_F: Bitboard = 0x0101_0101_0101_0101 << 5
-BB_FILE_G: Bitboard = 0x0101_0101_0101_0101 << 6
-BB_FILE_H: Bitboard = 0x0101_0101_0101_0101 << 7
+BB_FILE_A: Bitboard = 0x0101_0101_0101_0101 << FILE_A
+BB_FILE_B: Bitboard = 0x0101_0101_0101_0101 << FILE_B
+BB_FILE_C: Bitboard = 0x0101_0101_0101_0101 << FILE_C
+BB_FILE_D: Bitboard = 0x0101_0101_0101_0101 << FILE_D
+BB_FILE_E: Bitboard = 0x0101_0101_0101_0101 << FILE_E
+BB_FILE_F: Bitboard = 0x0101_0101_0101_0101 << FILE_F
+BB_FILE_G: Bitboard = 0x0101_0101_0101_0101 << FILE_G
+BB_FILE_H: Bitboard = 0x0101_0101_0101_0101 << FILE_H
 BB_FILES: List[Bitboard] = [BB_FILE_A, BB_FILE_B, BB_FILE_C, BB_FILE_D, BB_FILE_E, BB_FILE_F, BB_FILE_G, BB_FILE_H]
 
-BB_RANK_1: Bitboard = 0xff << (8 * 0)
-BB_RANK_2: Bitboard = 0xff << (8 * 1)
-BB_RANK_3: Bitboard = 0xff << (8 * 2)
-BB_RANK_4: Bitboard = 0xff << (8 * 3)
-BB_RANK_5: Bitboard = 0xff << (8 * 4)
-BB_RANK_6: Bitboard = 0xff << (8 * 5)
-BB_RANK_7: Bitboard = 0xff << (8 * 6)
-BB_RANK_8: Bitboard = 0xff << (8 * 7)
+BB_RANK_1: Bitboard = 0xff << (8 * RANK_1)
+BB_RANK_2: Bitboard = 0xff << (8 * RANK_2)
+BB_RANK_3: Bitboard = 0xff << (8 * RANK_3)
+BB_RANK_4: Bitboard = 0xff << (8 * RANK_4)
+BB_RANK_5: Bitboard = 0xff << (8 * RANK_5)
+BB_RANK_6: Bitboard = 0xff << (8 * RANK_6)
+BB_RANK_7: Bitboard = 0xff << (8 * RANK_7)
+BB_RANK_8: Bitboard = 0xff << (8 * RANK_8)
 BB_RANKS: List[Bitboard] = [BB_RANK_1, BB_RANK_2, BB_RANK_3, BB_RANK_4, BB_RANK_5, BB_RANK_6, BB_RANK_7, BB_RANK_8]
 
 BB_BACKRANKS: Bitboard = BB_RANK_1 | BB_RANK_8
@@ -1847,7 +1867,7 @@ def generate_pseudo_legal_moves(self, from_mask: Bitboard = BB_ALL, to_mask: Bit
                 self.occupied_co[not self.turn] & to_mask)
 
             for to_square in scan_reversed(targets):
-                if square_rank(to_square) in [0, 7]:
+                if square_rank(to_square) in [RANK_1, RANK_8]:
                     yield Move(from_square, to_square, QUEEN)
                     yield Move(from_square, to_square, ROOK)
                     yield Move(from_square, to_square, BISHOP)
@@ -1870,7 +1890,7 @@ def generate_pseudo_legal_moves(self, from_mask: Bitboard = BB_ALL, to_mask: Bit
         for to_square in scan_reversed(single_moves):
             from_square = to_square + (8 if self.turn == BLACK else -8)
 
-            if square_rank(to_square) in [0, 7]:
+            if square_rank(to_square) in [RANK_1, RANK_8]:
                 yield Move(from_square, to_square, QUEEN)
                 yield Move(from_square, to_square, ROOK)
                 yield Move(from_square, to_square, BISHOP)
@@ -1897,7 +1917,7 @@ def generate_pseudo_legal_ep(self, from_mask: Bitboard = BB_ALL, to_mask: Bitboa
         capturers = (
             self.pawns & self.occupied_co[self.turn] & from_mask &
             BB_PAWN_ATTACKS[not self.turn][self.ep_square] &
-            BB_RANKS[4 if self.turn else 3])
+            BB_RANKS[RANK_5 if self.turn else RANK_4])
 
         for capturer in scan_reversed(capturers):
             yield Move(capturer, self.ep_square)
@@ -1977,9 +1997,9 @@ def is_pseudo_legal(self, move: Move) -> bool:
             if piece != PAWN:
                 return False
 
-            if self.turn == WHITE and square_rank(move.to_square) != 7:
+            if self.turn == WHITE and square_rank(move.to_square) != RANK_8:
                 return False
-            elif self.turn == BLACK and square_rank(move.to_square) != 0:
+            elif self.turn == BLACK and square_rank(move.to_square) != RANK_1:
                 return False
 
         # Handle castling.
@@ -2401,18 +2421,18 @@ def push(self, move: Move) -> None:
             else:
                 self.castling_rights &= ~BB_RANK_8
         elif captured_piece_type == KING and not self.promoted & to_bb:
-            if self.turn == WHITE and square_rank(move.to_square) == 7:
+            if self.turn == WHITE and square_rank(move.to_square) == RANK_8:
                 self.castling_rights &= ~BB_RANK_8
-            elif self.turn == BLACK and square_rank(move.to_square) == 0:
+            elif self.turn == BLACK and square_rank(move.to_square) == RANK_1:
                 self.castling_rights &= ~BB_RANK_1
 
         # Handle special pawn moves.
         if piece_type == PAWN:
             diff = move.to_square - move.from_square
 
-            if diff == 16 and square_rank(move.from_square) == 1:
+            if diff == 16 and square_rank(move.from_square) == RANK_2:
                 self.ep_square = move.from_square + 8
-            elif diff == -16 and square_rank(move.from_square) == 6:
+            elif diff == -16 and square_rank(move.from_square) == RANK_7:
                 self.ep_square = move.from_square - 8
             elif move.to_square == ep_square and abs(diff) in [7, 9] and not captured_piece_type:
                 # Remove pawns captured en passant.
@@ -3605,11 +3625,11 @@ def _valid_ep_square(self) -> Optional[Square]:
             return None
 
         if self.turn == WHITE:
-            ep_rank = 5
+            ep_rank = RANK_6
             pawn_mask = shift_down(BB_SQUARES[self.ep_square])
             seventh_rank_mask = shift_up(BB_SQUARES[self.ep_square])
         else:
-            ep_rank = 2
+            ep_rank = RANK_3
             pawn_mask = shift_up(BB_SQUARES[self.ep_square])
             seventh_rank_mask = shift_down(BB_SQUARES[self.ep_square])
 

chess/gaviota.py

@@ -110,12 +110,12 @@ def idx_is_empty(x: int) -> int:
 def flip_type(x: chess.Square, y: chess.Square) -> int:
     ret = 0
 
-    if chess.square_file(x) > 3:
+    if chess.square_file(x) > chess.FILE_D:
         x = flip_we(x)
         y = flip_we(y)
         ret |= 1
 
-    if chess.square_rank(x) > 3:
+    if chess.square_rank(x) > chess.RANK_4:
         x = flip_ns(x)
         y = flip_ns(y)
         ret |= 2
@@ -351,11 +351,11 @@ def init_ppidx() -> Tuple[List[List[int]], List[int], List[int]]:
 
 
 def norm_kkindex(x: chess.Square, y: chess.Square) -> Tuple[int, int]:
-    if chess.square_file(x) > 3:
+    if chess.square_file(x) > chess.FILE_D:
         x = flip_we(x)
         y = flip_we(y)
 
-    if chess.square_rank(x) > 3:
+    if chess.square_rank(x) > chess.RANK_4:
         x = flip_ns(x)
         y = flip_ns(y)
 

chess/syzygy.py

@@ -761,7 +761,7 @@ def calc_symlen(self, d: PairsData, s: int, tmp: List[int]) -> None:
             d.symlen[s] = d.symlen[s1] + d.symlen[s2] + 1
         tmp[s] = 1
 
-    def pawn_file(self, pos: List[chess.Square]) -> int:
+    def pawn_file(self, pos: List[chess.Square]) -> chess.File:
         for i in range(1, self.pawns[0]):
             if FLAP[pos[0]] > FLAP[pos[i]]:
                 pos[0], pos[i] = pos[i], pos[0]