UndefinedOperationError for calls to game.nodes and game.sort_infosets on non-trees

Author: rahulsavani

src/pygambit/game.pxi

@@ -742,7 +742,16 @@ class Game:
         .. versionchanged:: 16.4
            Changed from a method ``nodes()`` to a property.
 
+        Raises
+        ------
+        UndefinedOperationError
+            If the game does not have a tree representation.
         """
+        if not self.is_tree:
+            raise UndefinedOperationError(
+                "Operation only defined for games with a tree representation"
+            )
+
         return GameNodes.wrap(self.game)
 
     @property
@@ -1885,11 +1894,20 @@ class Game:
 
         .. versionadded:: 16.4.0
 
+        Raises
+        ------
+        UndefinedOperationError
+            If the game does not have a tree representation.
+
         See also
         --------
         Player.infosets
         Infoset.members
         """
+        if not self.is_tree:
+            raise UndefinedOperationError(
+                "Operation only defined for games with a tree representation"
+            )
         self.game.deref().SortInfosets()
 
     def add_player(self, label: str = "") -> Player:

tests/test_strategic.py

@@ -37,7 +37,14 @@ def test_strategic_game_root():
 
 def test_strategic_game_nodes():
     game = gbt.Game.new_table([2, 2])
-    assert list(game.nodes) == []
+    with pytest.raises(gbt.UndefinedOperationError):
+        _ = game.nodes
+
+
+def test_strategic_game_sort_infosets():
+    game = gbt.Game.new_table([2, 2])
+    with pytest.raises(gbt.UndefinedOperationError):
+        _ = game.sort_infosets()
 
 
 def test_game_behav_profile_error():