Merge pull request #505 from marcharper/504

Catch self.plays == 0 corner case of LookerUp

Author: marcharper

axelrod/strategies/lookerup.py

@@ -122,11 +122,15 @@ def strategy(self, opponent):
         if len(self.history) < max(self.plays, self.opponent_start_plays):
             return C
         # Count backward m turns to get my own recent history.
-        history_start = -1 * self.plays
-        my_history = ''.join(self.history[history_start:])
-        # Do the same for the opponent.
-        opponent_history = ''.join(opponent.history[history_start:])
-        # Get the opponents first n actions.
+        if self.plays == 0:
+            my_history = ''
+            opponent_history = ''
+        else:
+            history_start = -1 * self.plays
+            my_history = ''.join(self.history[history_start:])
+            # Do the same for the opponent.
+            opponent_history = ''.join(opponent.history[history_start:])
+            # Get the opponents first n actions.
         opponent_start = ''.join(opponent.history[:self.opponent_start_plays])
         # Put these three strings together in a tuple.
         key = (opponent_start, my_history, opponent_history)

axelrod/tests/unit/test_lookerup.py

@@ -2,6 +2,7 @@
 
 import axelrod
 from .test_player import TestPlayer, TestHeadsUp
+from axelrod.strategies.lookerup import create_lookup_table_keys
 
 C, D = axelrod.Actions.C, axelrod.Actions.D
 
@@ -66,6 +67,21 @@ def test_defector_table(self):
         self.responses_test([C, D], [D, C], [D])
         self.responses_test([D, D], [D, D], [D])
 
+    def test_zero_tables(self):
+        """Test the corner case where n=0."""
+        pattern = "CD"
+        lookup_table_keys = create_lookup_table_keys(plays=0,
+                                                     opponent_start_plays=1)
+
+        lookup_table = dict(zip(lookup_table_keys, pattern))
+        player = axelrod.LookerUp(lookup_table)
+        self.assertEqual(player.plays, 0)
+        opp = axelrod.Cooperator()
+        # This shouldn't throw an exception.
+        for _ in range(5):
+            player.play(opp)
+
+
     def test_starting_move(self):
         """A lookup table that always repeats the opponent's first move."""