Ignore up to one consecutive empty line between PGN headers (fixes ni…

…klasf#566)

chess/pgn.py

@@ -1226,12 +1226,19 @@ def read_game(handle: TextIO, *, Visitor = GameBuilder):
         line = handle.readline()
 
     # Parse game headers.
+    consecutive_empty_lines = 0
     while line:
         # Ignore comments.
         if line.startswith("%") or line.startswith(";"):
             line = handle.readline()
             continue
 
+        # Ignore up to one consecutive empty line between headers.
+        if consecutive_empty_lines < 1 and line.isspace():
+            consecutive_empty_lines += 1
+            line = handle.readline()
+            continue
+
         # First token of the game.
         if not found_game:
             found_game = True
@@ -1244,6 +1251,8 @@ def read_game(handle: TextIO, *, Visitor = GameBuilder):
         if not line.startswith("["):
             break
 
+        consecutive_empty_lines = 0
+
         if not skipping_game:
             tag_match = TAG_REGEX.match(line)
             if tag_match:
@@ -1261,10 +1270,6 @@ def read_game(handle: TextIO, *, Visitor = GameBuilder):
     if not skipping_game:
         skipping_game = visitor.end_headers() is SKIP
 
-    # Ignore single empty line after headers.
-    if line.isspace():
-        line = handle.readline()
-
     if not skipping_game:
         # Chess variant.
         headers = managed_headers if unmanaged_headers is None else unmanaged_headers

data/pgn/chessbase-empty-line.pgn

@@ -0,0 +1,35 @@
+[Event "AlphaZero vs. Stockfish"]
+
+[Date "2017.12.04"]
+[Round "1"]
+[White "Stockfish 8"]
+[Black "AlphaZero"]
+[Result "0-1"]
+[Board "1"]
+[WhiteCountry "NOR"]
+[WhiteFideId "stockfish"]
+[BlackCountry "ENG"]
+[BlackFideId "deepmind"]
+
+1. e4  e5  2. Nf3  Nc6  3. Bb5  Nf6  4. d3  Bc5
+ 5. Bxc6  dxc6  6. O-O  Nd7  7. Nbd2  O-O  8.
+Qe1  f6  9. Nc4  Rf7  10. a4  Bf8  11. Kh1 
+Nc5  12. a5  Ne6  13. Ncxe5
+ fxe5  14. Nxe5  Rf6  15. Ng4  Rf7  16. Ne5 
+Re7  17. a6  c5  18. f4  Qe8  19. axb7  Bxb7 
+20. Qa5  Nd4  21. Qc3  Re6  22. Be3  Rb6  23. Nc4 
+Rb4  24. b3  a5  25. Rxa5  Rxa5  26. Nxa5  Ba6 
+27. Bxd4  Rxd4  28. Nc4  Rd8
+ 29. g3  h6  30. Qa5  Bc8  31. Qxc7  Bh3  32.
+Rg1  Rd7  33. Qe5  Qxe5  34. Nxe5  Ra7  35. Nc4 
+g5  36. Rc1  Bg7  37. Ne5  Ra8  38. Nf3  Bb2  39.
+Rb1  Bc3  40. Ng1  Bd7  41. Ne2  Bd2  42. Rd1 
+Be3  43. Kg2  Bg4  44. Re1  Bd2  45. Rf1  Ra2  46.
+h3  Bxe2  47. Rf2  Bxf4  48. Rxe2  Be5  49. Rf2 
+Kg7  50. g4  Bd4  51. Re2  Kf6  52. e5+  Bxe5  53.
+Kf3  Ra1  54. Rf2  Re1  55. Kg2+  Bf4  56. c3 
+Rc1  57. d4  Rxc3  58. dxc5
+ Rxc5  59. b4  Rc3  60. h4  Ke5  61. hxg5 
+hxg5  62. Re2+  Kf6  63. Kf2
+ Be5  64. Ra2  Rc4  65. Ra6+  Ke7  66. Ra5 
+Ke6  67. Ra6+  Bd6  0-1

test.py

@@ -2456,6 +2456,15 @@ def test_missing_setup_tag(self):
         board = chess.Board("rbb1N1k1/pp1n1ppp/8/2Pp4/3P4/4P3/P1Q2PPq/R1BR1K2 b - - 0 1")
         self.assertEqual(game.board(), board)
 
+    def test_chessbase_empty_line(self):
+        with open("data/pgn/chessbase-empty-line.pgn") as pgn:
+            game = chess.pgn.read_game(pgn)
+            self.assertEqual(game.headers["Event"], "AlphaZero vs. Stockfish")
+            self.assertEqual(game.headers["Round"], "1")
+            self.assertEqual(game.variations[0].move, chess.Move.from_uci("e2e4"))
+
+            self.assertTrue(chess.pgn.read_game(pgn) is None)
+
     def test_game_from_board(self):
         setup = "3k4/8/4K3/8/8/8/8/2R5 b - - 0 1"
         board = chess.Board(setup)