Update cycle detection to be more efficient (#809)

* Update cycle detection to be more efficient
* PEP8 spacing fix

axelrod/_strategy_utils.py

@@ -10,7 +10,7 @@
 C, D = Actions.C, Actions.D
 
 
-def detect_cycle(history, min_size=1, offset=0):
+def detect_cycle(history, min_size=1, max_size=12, offset=0):
     """Detects cycles in the sequence history.
 
     Mainly used by hunter strategies.
@@ -21,18 +21,22 @@ def detect_cycle(history, min_size=1, offset=0):
         The sequence to look for cycles within
     min_size: int, 1
         The minimum length of the cycle
+    max_size: int, 12
     offset: int, 0
         The amount of history to skip initially
     """
-    history_tail = history[-offset:]
-    for i in range(min_size, len(history_tail) // 2):
+    history_tail = history[offset:]
+    max_ = min(len(history_tail) // 2, max_size)
+    for i in range(min_size, max_):
+        has_cycle = True
         cycle = tuple(history_tail[:i])
         for j, elem in enumerate(history_tail):
             if elem != cycle[j % len(cycle)]:
+                has_cycle = False
                 break
-        if j == len(history_tail) - 1:
+        if has_cycle and (j == len(history_tail) - 1):
             # We made it to the end, is the cycle itself a cycle?
-            # I.E. CCC is not ok as cycle if min_size is really 2
+            # E.G. CCC is not ok as cycle if min_size is really 2
             # Since this is the same as C
             return cycle
     return None

axelrod/strategies/hunter.py

@@ -44,6 +44,13 @@ def strategy(self, opponent):
         return C
 
 
+def is_alternator(history):
+    for i in range(len(history) - 1):
+        if history[i] == history[i + 1]:
+            return False
+    return True
+
+
 class AlternatorHunter(Player):
     """A player who hunts for alternators."""
 
@@ -58,12 +65,24 @@ class AlternatorHunter(Player):
         'manipulates_state': False
     }
 
+    def __init__(self):
+        Player.__init__(self)
+        self.is_alt = False
+
     def strategy(self, opponent):
-        oh = opponent.history
-        if len(self.history) >= 6 and all([oh[i] != oh[i+1] for i in range(len(oh)-1)]):
+        if len(opponent.history) < 6:
+            return C
+        if len(self.history) == 6:
+            if is_alternator(opponent.history):
+                self.is_alt = True
+        if self.is_alt:
             return D
         return C
 
+    def reset(self):
+        Player.reset(self)
+        self.is_alt = False
+
 
 class CycleHunter(Player):
     """Hunts strategies that play cyclically, like any of the Cyclers,
@@ -80,36 +99,40 @@ class CycleHunter(Player):
         'manipulates_state': False
     }
 
-    @staticmethod
-    def strategy(opponent):
-        cycle = detect_cycle(opponent.history, min_size=2)
+    def __init__(self):
+        Player.__init__(self)
+        self.cycle = None
+
+    def strategy(self, opponent):
+        if self.cycle:
+            return D
+        cycle = detect_cycle(opponent.history, min_size=3)
         if cycle:
             if len(set(cycle)) > 1:
+                self.cycle = cycle
                 return D
         return C
 
+    def reset(self):
+        Player.reset(self)
+        self.cycle = None
 
-class EventualCycleHunter(Player):
-    """Hunts strategies that eventually play cyclically"""
+
+class EventualCycleHunter(CycleHunter):
+    """Hunts strategies that eventually play cyclically."""
 
     name = 'Eventual Cycle Hunter'
-    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
-    }
 
-    @staticmethod
-    def strategy(opponent):
+    def strategy(self, opponent):
         if len(opponent.history) < 10:
             return C
         if len(opponent.history) == opponent.cooperations:
             return C
-        if detect_cycle(opponent.history, offset=15):
+        if len(opponent.history) % 10 == 0:
+            # recheck
+            self.cycle = detect_cycle(opponent.history, offset=10,
+                                      min_size=3)
+        if self.cycle:
             return D
         else:
             return C

axelrod/strategies/memoryone.py

@@ -3,6 +3,7 @@
 
 C, D = Actions.C, Actions.D
 
+
 class MemoryOnePlayer(Player):
     """Uses a four-vector for strategies based on the last round of play,
     (P(C|CC), P(C|CD), P(C|DC), P(C|DD)), defaults to Win-Stay Lose-Shift.

axelrod/tests/unit/test_hunter.py

@@ -89,12 +89,20 @@ class TestAlternatorHunter(TestPlayer):
 
     def test_strategy(self):
         self.first_play_test(C)
-        self.responses_test([C] * 2, [C, D], [C])
-        self.responses_test([C] * 3, [C, D, C], [C])
-        self.responses_test([C] * 4, [C, D] * 2, [C])
-        self.responses_test([C] * 5, [C, D] * 2 + [C], [C])
-        self.responses_test([C] * 6, [C, D] * 3, [D])
-        self.responses_test([C] * 7, [C, D] * 3 + [C], [D])
+        self.responses_test([C] * 2, [C, D], [C], attrs={'is_alt': False})
+        self.responses_test([C] * 3, [C, D, C], [C], attrs={'is_alt': False})
+        self.responses_test([C] * 4, [C, D] * 2, [C], attrs={'is_alt': False})
+        self.responses_test([C] * 5, [C, D] * 2 + [C], [C],
+                            attrs={'is_alt': False})
+        self.responses_test([C] * 6, [C, D] * 3, [D], attrs={'is_alt': True})
+        self.responses_test([C] * 7, [C, D] * 3 + [C], [D],
+                            attrs={'is_alt': True})
+
+    def test_reset_attr(self):
+        p = self.player()
+        p.is_alt = True
+        p.reset()
+        self.assertFalse(p.is_alt)
 
 
 class TestCycleHunter(TestPlayer):
@@ -122,18 +130,25 @@ def test_strategy(self):
                 player.play(opponent)
             self.assertEqual(player.history[-1], D)
         # Test against non-cyclers
+        axelrod.seed(40)
         for opponent in [axelrod.Random(), axelrod.AntiCycler(),
                          axelrod.Cooperator(), axelrod.Defector()]:
             player.reset()
             for i in range(30):
                 player.play(opponent)
             self.assertEqual(player.history[-1], C)
 
+    def test_reset_attr(self):
+        p = self.player()
+        p.cycle = "CCDDCD"
+        p.reset()
+        self.assertEqual(p.cycle, None)
+
 
 class TestEventualCycleHunter(TestPlayer):
 
-    name = "Cycle Hunter"
-    player = axelrod.CycleHunter
+    name = "Eventual Cycle Hunter"
+    player = axelrod.EventualCycleHunter
     expected_classifier = {
         'memory_depth': float('inf'),  # Long memory
         'stochastic': False,
@@ -155,13 +170,20 @@ def test_strategy(self):
                 player.play(opponent)
             self.assertEqual(player.history[-1], D)
         # Test against non-cyclers and cooperators
+        axelrod.seed(43)
         for opponent in [axelrod.Random(), axelrod.AntiCycler(),
                          axelrod.DoubleCrosser(), axelrod.Cooperator()]:
             player.reset()
             for i in range(50):
                 player.play(opponent)
             self.assertEqual(player.history[-1], C)
 
+    def test_reset_attr(self):
+        p = self.player()
+        p.cycle = "CCDDCD"
+        p.reset()
+        self.assertEqual(p.cycle, None)
+
 
 class TestMathConstantHunter(TestPlayer):
 

axelrod/tests/unit/test_prober.py

@@ -299,7 +299,7 @@ def test_remorse(self):
         opponent = axelrod.Cooperator()
 
         test_responses(self, player, opponent, [C], [C], [C],
-                       random_seed=0, attrs={'probing': False})
+                       random_seed=3, attrs={'probing': False})
 
         test_responses(self, player, opponent, [C], [C], [D],
                        random_seed=1, attrs={'probing': True})