Add GrudgerAlternator strategy

Author: geraintpalmer

axelrod/strategies/_strategies.py

@@ -29,7 +29,7 @@
     HardGoByMajority5)
 from .gradualkiller import GradualKiller
 from .grudger import (Grudger, ForgetfulGrudger, OppositeGrudger, Aggravater,
-    SoftGrudger)
+    SoftGrudger, GrudgerAlternator)
 from .grumpy import Grumpy
 from .handshake import Handshake
 from .hunter import (
@@ -124,6 +124,7 @@
     GradualKiller,
     Grofman,
     Grudger,
+    GrudgerAlternator,
     Grumpy,
     Handshake,
     HardGoByMajority,

axelrod/strategies/grudger.py

@@ -171,3 +171,33 @@ def reset(self):
         Player.reset(self)
         self.grudged = False
         self.grudge_memory = 0
+
+
+
+class GrudgerAlternator(Player):
+    """
+    A player starts by cooperating until the first opponents defenction,
+    then alternates D-C.
+
+    Names:
+
+    - c_then_per_dc: [PRISON1998]_
+    """
+
+    name = 'GrudgerAlternator'
+    classifier = {
+        'memory_depth': float('inf'),  # Long memory
+        'stochastic': False,
+        'makes_use_of': set(),
+        'long_run_time': False,
+        'inspects_source': False,
+        'manipulates_source': False,
+        'manipulates_state': False
+    }
+
+    def strategy(self, opponent):
+        """Begins by playing C, then plays Alternator for the remaining rounds if the opponent ever plays D."""
+        if opponent.defections:
+            if self.history[-1] == Actions.C:
+                return Actions.D
+        return Actions.C

axelrod/tests/unit/test_grudger.py

@@ -1,6 +1,7 @@
 """Tests for grudger strategies."""
 
 import axelrod
+from random import randint
 
 from .test_player import TestPlayer
 
@@ -173,3 +174,56 @@ def test_reset(self):
         p.reset()
         self.assertFalse(p.grudged)
         self.assertEqual(p.grudge_memory, 0)
+
+
+
+class TestGrudgerAlternator(TestPlayer):
+
+    name = "GrudgerAlternator"
+    player = axelrod.GrudgerAlternator
+    expected_classifier = {
+        'memory_depth': float('inf'),  # Long memory
+        'stochastic': False,
+        'makes_use_of': set(),
+        'long_run_time': False,
+        'inspects_source': False,
+        'manipulates_source': False,
+        'manipulates_state': False
+    }
+
+    def test_initial_strategy(self):
+        """
+        Starts by cooperating
+        """
+        self.first_play_test(C)
+
+    def test_strategy(self):
+        """
+        If opponent defects at any point then the player will alternate D-C.
+        """
+        self.responses_test([C, C, C, C, C], [C, C, C, C, C], [C])
+        self.responses_test([C, C, C, C, C, C], [C, C, C, C, C, D], [D])
+        self.responses_test([C, C, C, C, C, C, D], [C, C, C, C, C, D, D], [C])
+        self.responses_test([C, C, C, C, C, C, D, C], [C, C, C, C, C, D, D, C], [D])
+        self.responses_test([C, C, C, C, C, C, D, C, D], [C, C, C, C, C, D, D, C, C], [C])
+
+    def test_starategy_random_number_rounds(self):
+        """
+        Runs test_strategy for a random number of rounds
+        """
+        # Hasn't defected yet
+        for _  in range(20):
+            i = randint(1, 30)
+            j = randint(1, 30)
+            opp_hist = [C] * i
+            my_hist = [C] * i
+            self.responses_test(my_hist, opp_hist, [C]*j)
+
+        # Defected at least once
+        for _ in range(20):
+            i = randint(1, 30)
+            j = randint(1, 30)
+            opp_hist = [C for r in range(i)] + [D]
+            my_hist = [C] * (i + 1)
+            expected_response = [D if r % 2 == 0 else C for r in range(j)]
+            self.responses_test(my_hist, opp_hist, expected_response)