Update documentation and Python tests to reflect new conventions.

src/games/gametree.cc

@@ -1034,18 +1034,24 @@ int GameTreeRep::NumNodes() const
 
 Game GameTreeRep::SetChanceProbs(const GameInfoset &p_infoset, const Array<Number> &p_probs)
 {
+  if (p_infoset->GetGame() != this) {
+    throw MismatchException();
+  }
   if (!p_infoset->IsChanceInfoset()) {
-    throw UndefinedException();
+    throw UndefinedException("Action probabilities can only be specified for chance information sets");
   }
   if (p_infoset->NumActions() != p_probs.size()) {
-    throw DimensionException();
+    throw DimensionException("The number of probabilities given must match the number of actions");
   }
   Rational sum(0);
   for (auto prob : p_probs) {
+    if (static_cast<Rational>(prob) < Rational(0)) {
+      throw ValueException("Probabilities must be non-negative numbers");
+    }
     sum += static_cast<Rational>(prob);
   }
   if (sum != Rational(1)) {
-    throw ValueException();
+    throw ValueException("Probabilities must sum to exactly one");
   }
   for (int act = 1; act <= p_infoset->NumActions(); act++) {
     dynamic_cast<GameTreeInfosetRep &>(*p_infoset).m_probs[act] = p_probs[act];

src/pygambit/action.pxi

@@ -89,16 +89,19 @@ class Action:
     @property
     def prob(self) -> typing.Union[decimal.Decimal, Rational]:
         """
-        Get or set the probability a chance action is played.
-        When setting the probability, the value can be any numeric type, or any object that
-        has a string representation which can be interpreted as an integer,
-        decimal, or rational number.
+        Get the probability a chance action is played.
+
+        .. deprecated:: 16.1.0
+           Setting individual chance action probabilities is no longer supported.
+           Use `Game.set_chance_probs()` instead.
 
         Raises
         ------
-        ValueError
-            If `value` cannot be interpreted as a decimal or rational number.
+        UndefinedOperationError
+            If the action does not belong to the chance player.
         """
+        if not self.infoset.is_chance:
+            raise UndefinedOperationError("action probabilities are only defined at chance information sets")
         py_string = cython.cast(
             string,
             self.action.deref().GetInfoset().deref().GetActionProb(self.action.deref().GetNumber())
@@ -110,6 +113,4 @@ class Action:
 
     @prob.setter
     def prob(self, value: typing.Any) -> None:
-        self.action.deref().GetInfoset().deref().SetActionProb(
-            self.action.deref().GetNumber(), _to_number(value)
-        )
+        raise UndefinedOperationError("use Game.set_chance_probs() to set probabilities at chance information sets")

src/pygambit/game.pxi

@@ -515,8 +515,8 @@ class Game:
         IndexError
             If the length of `probs` is not the same as the number of actions at the information set
         ValueError
-            If any of the elements of `probs` are not interpretable as numbers, or the values of `probs` do not
-            sum to one.
+            If any of the elements of `probs` are not interpretable as numbers, or the values of `probs` are not
+            nonnegative numbers that sum to exactly one.
         """
         if infoset.game != self:
             raise MismatchError("set_chance_probs() first argument must be an infoset in the same game")
@@ -527,7 +527,10 @@ class Game:
         numbers = Array[c_Number](len(probs))
         for i in range(1, len(probs)+1):
             setitem_array_number(numbers, i, _to_number(probs[i-1]))
-        self.game.deref().SetChanceProbs(infoset.infoset, numbers)
+        try:
+            self.game.deref().SetChanceProbs(infoset.infoset, numbers)
+        except RuntimeError:
+            raise ValueError("set_chance_probs(): must specify non-negative probabilities that sum to one")
         return self
 
     def _get_contingency(self, *args):

src/pygambit/tests/test_actions.py

@@ -1,5 +1,4 @@
 import pygambit
-import decimal
 import fractions
 import unittest
 
@@ -22,53 +21,38 @@ def test_action_set_label(self):
             "action label"
         )
 
-    def test_action_probability(self):
-        """Test to ensure action probabilities work"""
-        assert (
-            self.extensive_game.root.infoset.actions[0].prob ==
-            decimal.Decimal('0.500000')
-        )
+    def test_action_probability_chance(self):
+        """Test setting action probabilities at chance information sets"""
+        assert (self.extensive_game.root.infoset.actions[0].prob == 0.5)
 
-        self.extensive_game.root.infoset.actions[0].prob = 2.0
-        assert (
-                self.extensive_game.root.infoset.actions[0].prob ==
-                fractions.Fraction(2)
-        )
+        self.extensive_game.set_chance_probs(self.extensive_game.root.infoset, [0.75, 0.25])
+        assert (self.extensive_game.root.infoset.actions[0].prob == 0.75)
+        assert (self.extensive_game.root.infoset.actions[1].prob == 0.25)
 
-        self.extensive_game.root.infoset.actions[0].prob = (
-            decimal.Decimal('0.97300')
-        )
-        assert (
-            self.extensive_game.root.infoset.actions[0].prob ==
-            decimal.Decimal('0.97300')
-        )
+        self.extensive_game.set_chance_probs(self.extensive_game.root.infoset, ["1/17", "16/17"])
+        assert (self.extensive_game.root.infoset.actions[0].prob == fractions.Fraction("1/17"))
+        assert (self.extensive_game.root.infoset.actions[1].prob == fractions.Fraction("16/17"))
 
-        self.extensive_game.root.infoset.actions[0].prob = (
-            fractions.Fraction('1/17')
+        self.assertRaises(
+            ValueError, self.extensive_game.set_chance_probs, self.extensive_game.root.infoset, [0.75, 0.10]
         )
-        assert (
-            self.extensive_game.root.infoset.actions[0].prob ==
-            fractions.Fraction('1/17')
+        self.assertRaises(
+            ValueError, self.extensive_game.set_chance_probs, self.extensive_game.root.infoset, [1.1, -0.1]
         )
-
-        self.extensive_game.root.infoset.actions[0].prob = 2
-        assert self.extensive_game.root.infoset.actions[0].prob == 2
-
-        self.extensive_game.root.infoset.actions[0].prob = "1/7"
-        assert (
-            self.extensive_game.root.infoset.actions[0].prob ==
-            fractions.Fraction('1/7')
+        self.assertRaises(
+            IndexError, self.extensive_game.set_chance_probs, self.extensive_game.root.infoset, [0.75, 0.10, 0.15]
         )
-
-        self.extensive_game.root.infoset.actions[0].prob = "2.7"
-        assert (
-            self.extensive_game.root.infoset.actions[0].prob ==
-            decimal.Decimal('2.7')
+        self.assertRaises(
+            ValueError, setattr, self.extensive_game.root.infoset.actions[0], "prob", "test"
         )
 
+        self.extensive_game.set_chance_probs(self.extensive_game.root.infoset, [0.50, 0.50])
+
+    def test_action_probability_nonchance(self):
+        """Test attempts to set action probabilities at non-chance information sets."""
         self.assertRaises(
-            ValueError, setattr, self.extensive_game.root.infoset.actions[0],
-            "prob", "test"
+            pygambit.UndefinedOperationError, self.extensive_game.set_chance_probs,
+            self.extensive_game.players[0].infosets[0], [0.75, 0.25]
         )
 
     def test_action_precedes(self):