Issue 522

ChangeLog

@@ -10,8 +10,9 @@
   been removed as planned. (#357)
 
 ### Added
-- Implement `GetPlays()` (C++) and `get_plays` (Python) to compute the set of terminal nodes consistent
-  with a node, information set, or action (#517)
+- Implement `GameRep::GetPlays` (C++) and `Node.plays`, `Infoset.plays`, and `Action.plays` (Python)
+  to compute the set of terminal nodes consistent with a node, information set, or action (#517)
+- Implement `GameRep::GetVeto` (C++) and `Action.veto` (Python) to compute the veto of an action (#522).
 
 
 ## [16.3.1] - unreleased

doc/pygambit.api.rst

@@ -169,6 +169,7 @@ Information about the game
    Action.precedes
    Action.prob
    Action.plays
+   Action.power
 
 .. autosummary::
 

src/games/game.h

@@ -558,6 +558,9 @@ class GameRep : public BaseGameRep {
   /// Returns the set of terminal nodes which are descendants of members of an action
   virtual std::vector<GameNode> GetPlays(GameAction action) const { throw UndefinedException(); }
 
+  /// Returns the power of an action
+  virtual std::vector<GameNode> GetVeto(GameAction action) const { throw UndefinedException(); }
+
   /// Returns true if the game is perfect recall.  If not,
   /// a pair of violating information sets is returned in the parameters.
   virtual bool IsPerfectRecall(GameInfoset &, GameInfoset &) const = 0;

src/games/gametree.cc

@@ -1058,6 +1058,19 @@ std::vector<GameNode> GameTreeRep::GetPlays(GameAction action) const
   return plays;
 }
 
+std::vector<GameNode> GameTreeRep::GetVeto(GameAction action) const
+{
+  std::vector<GameNode> veto;
+  const std::vector<GameNode> aplays = GetPlays(action);
+
+  for (const auto &node : GetPlays(action->GetInfoset())) {
+    if (!contains(aplays, node)) {
+      veto.push_back(node);
+    }
+  }
+  return veto;
+}
+
 void GameTreeRep::DeleteOutcome(const GameOutcome &p_outcome)
 {
   IncrementVersion();

src/games/gametree.h

@@ -147,6 +147,8 @@ class GameTreeRep : public GameExplicitRep {
   std::vector<GameNode> GetPlays(GameInfoset infoset) const override;
   std::vector<GameNode> GetPlays(GameAction action) const override;
 
+  std::vector<GameNode> GetVeto(GameAction action) const override;
+
   Game CopySubgame(GameNode) const override;
   //@}
 

src/pygambit/action.pxi

@@ -109,9 +109,18 @@ class Action:
 
     @property
     def plays(self) -> typing.List[Node]:
-        """Returns a list of all terminal `Node` objects consistent with it.
+        """Returns a list of all terminal `Node` objects consistent with the action.
         """
         return [
             Node.wrap(n) for n in
             self.action.deref().GetInfoset().deref().GetGame().deref().GetPlays(self.action)
         ]
+
+    @property
+    def veto(self) -> typing.List[Node]:
+        """Returns power of the action.
+        """
+        return [
+            Node.wrap(n) for n in
+            self.action.deref().GetInfoset().deref().GetGame().deref().GetVeto(self.action)
+        ]

src/pygambit/gambit.pxd

@@ -282,6 +282,7 @@ cdef extern from "games/game.h":
         stdvector[c_GameNode] GetPlays(c_GameNode) except +
         stdvector[c_GameNode] GetPlays(c_GameInfoset) except +
         stdvector[c_GameNode] GetPlays(c_GameAction) except +
+        stdvector[c_GameNode] GetVeto(c_GameAction) except +
         bool IsPerfectRecall() except +
 
         c_GameInfoset AppendMove(c_GameNode, c_GamePlayer, int) except +ValueError

tests/test_actions.py

@@ -143,3 +143,18 @@ def test_action_plays():
     }  # paths=[0, 1, 0], [0, 1]
 
     assert set(test_action.plays) == expected_set_of_plays
+
+
+def test_action_veto():
+    """Verify `action.veto` returns the action's veto
+    (terminal `Node` objects contained in the information set associated with this action
+    that cannot be reached from this action).
+    """
+    game = games.read_from_file("e01.efg")
+    list_infosets = list(game.infosets)
+
+    test_action = list_infosets[2].actions[0]  # members' paths=[0, 1, 0], [0, 1]
+
+    expected_set_of_plays = set(list_infosets[2].plays) - set(test_action.plays)
+
+    assert set(test_action.veto) == expected_set_of_plays