Added function to list possible moves

chess.py

@@ -1,3 +1,4 @@
+from itertools import product
 from unicodedata import lookup
 
 def cross(A, B):
@@ -17,6 +18,14 @@ init_positions = {"pawn"   : cross(files, pawn_ranks),
                   "king"   : cross("e",   home_ranks)
                  }
 
+def addv(sq, v):
+    return chr(ord(sq[0]) + v[0]) + str(int(sq[1]) + v[1])
+
+def addvs(sq, vectors):
+    return [addv(sq, v) for v in vectors]
+
+def negatevs(vectors):
+    return [(-a, -b) for a,b in vectors]
 
 class Piece:
     def __init__(self, color=None, piece=None):
@@ -75,6 +84,47 @@ class Game:
     def occupying(self, piece):
         return [sq for sq in squares if self.board[sq] == piece]
 
+    def possible_moves(self, sq):
+        def is_possible(target):
+            return target in squares and \
+                   self.board[target].color != self.board[sq].color
+        def are_possible(vecs):
+            r = []
+            sqrs = addvs(sq, vecs)
+            for s in sqrs:
+                if not is_possible(s):
+                    break
+                r.append(s)
+                if not self.is_empty(s):
+                    break
+            return r
+
+        def possible_rook():
+            rvecs = list(zip(range(1,8), [0]*7))
+            fvecs = [(b,a) for a,b in rvecs]
+            vecs = [rvecs, fvecs, negatevs(rvecs), negatevs(fvecs)]
+            return sum(map(are_possible, vecs), [])
+
+        def possible_bishop():
+            ldvecs   = list(zip(range(1,8), range(1,8)))
+            rdvecs   = list(zip(range(1,8), range(-1, -8, -1)))
+            vecs = [ldvecs, rdvecs, negatevs(ldvecs), negatevs(rdvecs)]
+            return sum(map(are_possible, vecs), [])
+
+        piece = self.board[sq].piece
+
+        if piece == "pawn":
+            pass
+        elif piece == "knight":
+            vecs =  list(product((1,-1), (2,-2)))
+            vecs += list(product((2,-2), (1,-1)))
+            return [sq for sq in addvs(sq, vecs) if is_possible(sq)]
+        elif piece == "rook":
+            return possible_rook()
+        elif piece == "bishop":
+            return possible_bishop()
+        elif piece == "queen":
+            return possible_bishop() + possible_rook()
 
 
 
@@ -82,7 +132,8 @@ def test():
     game = Game()
     assert len(squares) == 8**2
     assert sum(map(len, init_positions.values())) == 8*4
+    game.board["d4"] = Piece("black", "bishop")
     print(game)
-    print(game.occupying(Piece("white", "pawn")))
+    print (game.possible_moves("d4"))
 
 test()