Revise Tideman and Cheruzzi.

As noted by @id428 we were not giving a "true" fresh start so I've
implemented that. I also added the two final defections (when the game
length is known).

Author: drvinceknight

axelrod/strategies/_strategies.py

@@ -15,7 +15,7 @@
     RevisedDowning,
     FirstByShubik,
     FirstBySteinAndRapoport,
-    TidemanAndChieruzzi,
+    FirstByTidemanAndChieruzzi,
     FirstByTullock,
     FirstByAnonymous,
 )
@@ -424,7 +424,7 @@
     ThueMorse,
     ThueMorseInverse,
     Thumper,
-    TidemanAndChieruzzi,
+    FirstByTidemanAndChieruzzi,
     TitForTat,
     TitFor2Tats,
     SecondByTranquilizer,

axelrod/strategies/axelrod_first.py

@@ -764,12 +764,26 @@ def strategy(self, opponent: Player) -> Action:
             return opponent.history[-1]
 
 
-# TODO Need to check this one, a MoreTidemanAndChieruzzi existed in
-# axelrod_second
-class TidemanAndChieruzzi(Player):
+@FinalTransformer((D, D), name_prefix=None)
+class FirstByTidemanAndChieruzzi(Player):
     """
-    This strategy begins by playing Tit For Tat and then follows the following
-    rules:
+    Submitted to Axelrod's first tournament by Nicolas Tideman and Paula
+    Chieruzzi.
+
+    The description written in [Axelrod1980]_ is:
+
+    > "This rule begins with cooperation and tit for tat. However, when the
+    > other player finishes his second run of defec- tions, an extra punishment is
+    > instituted, and the number of punishing defections is increased by one with
+    > each run of the other's defections. The other player is given a fresh start
+    > if he is 10 or more points behind, if he has not just started a run of
+    > defections, if it has been at least 20 moves since a fresh start, if there
+    > are at least 10 moves remaining, and if the number of defections differs
+    > from a 50-50 random generator by at least 3.0 standard deviations. A fresh
+    > start involves two cooperations and then play as if the game had just
+    > started. The program defects automatically on the last two moves."
+
+    This is interpreted as:
 
     1. Every run of defections played by the opponent increases the number of
     defections that this strategy retaliates with by 1.
@@ -782,8 +796,10 @@ class TidemanAndChieruzzi(Player):
         - and the total number of defections differs from a 50-50 random sample
           by at least 3.0 standard deviations.
 
-    A ‘fresh start’ is a sequence of two cooperations followed by an assumption
-    that the game has just started (everything is forgotten).
+        A ‘fresh start’ is a sequence of two cooperations followed by an assumption
+        that the game has just started (everything is forgotten).
+
+    3. The strategy defects on the last two moves.
 
     This strategy came 2nd in Axelrod’s original tournament.
 
@@ -792,7 +808,7 @@ class TidemanAndChieruzzi(Player):
     - TidemanAndChieruzzi: [Axelrod1980]_
     """
 
-    name = "Tideman and Chieruzzi"
+    name = "First tournament by Tideman and Chieruzzi"
     classifier = {
         "memory_depth": float("inf"),
         "stochastic": False,
@@ -812,6 +828,7 @@ def __init__(self) -> None:
         self.opponent_score = 0
         self.last_fresh_start = 0
         self.fresh_start = False
+        self.remembered_number_of_opponent_defectioons = 0
 
     def _decrease_retaliation_counter(self):
         """Lower the remaining owed retaliation count and flip to non-retaliate
@@ -826,6 +843,7 @@ def _fresh_start(self):
         self.is_retaliating = False
         self.retaliation_length = 0
         self.retaliation_remaining = 0
+        self.remembered_number_of_opponent_defectioons = 0
 
     def _score_last_round(self, opponent: Player):
         """Updates the scores for each player."""
@@ -840,6 +858,9 @@ def strategy(self, opponent: Player) -> Action:
         if not opponent.history:
             return C
 
+        if opponent.history[-1] == D:
+            self.remembered_number_of_opponent_defectioons += 1
+
         # Calculate the scores.
         self._score_last_round(opponent)
 
@@ -867,7 +888,8 @@ def strategy(self, opponent: Player) -> Action:
                 std_deviation = (N ** (1 / 2)) / 2
                 lower = N / 2 - 3 * std_deviation
                 upper = N / 2 + 3 * std_deviation
-                if opponent.defections <= lower or opponent.defections >= upper:
+                if (self.remembered_number_of_opponent_defectioons <= lower or
+                    self.remembered_number_of_opponent_defectioons >= upper):
                     # Opponent deserves a fresh start
                     self.last_fresh_start = current_round
                     self._fresh_start()

axelrod/tests/strategies/test_axelrod_first.py

@@ -553,10 +553,10 @@ def test_strategy(self):
         )
 
 
-class TestTidemanAndChieruzzi(TestPlayer):
+class TestFirstByTidemanAndChieruzzi(TestPlayer):
 
-    name = "Tideman and Chieruzzi"
-    player = axelrod.TidemanAndChieruzzi
+    name = "First tournament by Tideman and Chieruzzi: (D, D)"
+    player = axelrod.FirstByTidemanAndChieruzzi
     expected_classifier = {
         "memory_depth": float("inf"),
         "stochastic": False,
@@ -570,9 +570,15 @@ class TestTidemanAndChieruzzi(TestPlayer):
     def test_strategy(self):
         # Cooperator Test
         opponent = axelrod.Cooperator()
-        actions = [(C, C), (C, C), (C, C), (C, C)]
+        actions = [(C, C), (C, C), (D, C), (D, C)]
         self.versus_test(opponent, expected_actions=actions)
 
+        # Cooperator Test does noot defect if game length is unknown
+        opponent = axelrod.Cooperator()
+        actions = [(C, C), (C, C), (C, C), (C, C)]
+        self.versus_test(opponent, expected_actions=actions,
+                match_attributes={"length": float("inf")})
+
         # Defector Test
         opponent = axelrod.Defector()
         actions = [(C, D), (D, D), (D, D), (D, D)]
@@ -589,7 +595,7 @@ def test_strategy(self):
             (D, C),
             (D, D),
             (D, C),
-            (C, D),
+            (D, D),
             (D, C),
         ]
         self.versus_test(
@@ -743,7 +749,7 @@ def test_strategy(self):
             (D, D),
             (D, D),
             (D, C),
-            (C, D),
+            (D, D),
             (D, D),
         ]
 
@@ -753,7 +759,7 @@ def test_strategy(self):
 
         # Check the fresh start condition
         opponent = axelrod.TitForTat()
-        actions = [(C, C), (C, C), (C, C), (C, C)]
+        actions = [(C, C), (C, C), (D, C), (D, D)]
         self.versus_test(
             opponent, expected_actions=actions, attrs={"fresh_start": False}
         )
@@ -794,16 +800,16 @@ def test_strategy(self):
             (D, C),
             (D, C),
             (C, C),
-            (C, C),
-            (C, D),
+            (D, C),
+            (D, D),
         ]
         self.versus_test(
             opponent,
             expected_actions=actions,
             match_attributes={"length": 35},
             attrs={
-                "current_score": 108,
-                "opponent_score": 78,
+                "current_score": 110,
+                "opponent_score": 75,
                 "last_fresh_start": 24,
                 "retaliation_length": 2,
                 "retaliation_remaining": 0,

docs/reference/overview_of_strategies.rst

@@ -17,7 +17,7 @@ An indication is given as to whether or not this strategy is implemented in the
   :header: "Name", "Author", "Axelrod Library Name"
 
   "Tit For Tat", "Anatol Rapoport", ":class:`TitForTat <axelrod.strategies.titfortat.TitForTat>`"
-  "Tideman and Chieruzzi", "T Nicolaus Tideman and Paula Chieruzz", ":class:`TidemanAndChieruzzi <axelrod.strategies.axelrod_first.TidemanAndChieruzzi>`"
+  "Tideman and Chieruzzi", "T Nicolaus Tideman and Paula Chieruzz", ":class:`TidemanAndChieruzzi <axelrod.strategies.axelrod_first.FirstByTidemanAndChieruzzi>`"
   "Nydegger", "Rudy Nydegger", ":class:`Nydegger <axelrod.strategies.axelrod_first.FirstByNydegger>`"
   "Grofman", "Bernard Grofman", ":class:`Grofman <axelrod.strategies.axelrod_first.FirstByGrofman>`"
   "Shubik", "Martin Shubik", ":class:`Shubik <axelrod.strategies.axelrod_first.FirstByShubik>`"