@@ -566,3 +566,155 @@ def strategy(self, opponent: Player) -> Action:
566566 return one_move_ago
567567 else :
568568 return one_move_ago .flip ()
569+
570+ class Borufsen (Player ):
571+ """
572+ Strategy submitted to Axelrod's second tournament by Otto Borufsen
573+ (K32R), and came in third in that tournament.
574+
575+ This player keeps track of the the opponent's responses to own behavior:
576+
577+ - `cd_count` counts: Opponent cooperates as response to player defecting.
578+ - `cc_count` counts: Opponent cooperates as response to player cooperating.
579+
580+ The player has a defect mode and a normal mode. In defect mode, the
581+ player will always defect. In normal mode, the player obeys the following
582+ ranked rules:
583+
584+ 1. If in the last three turns, both the player/opponent defected, then
585+ cooperate for a single turn.
586+ 2. If in the last three turns, the player/opponent acted differently from
587+ each other and they're alternating, then change next defect to
588+ cooperate. (Doesn't block third rule.)
589+ 3. Otherwise, do tit-for-tat.
590+
591+ Start in normal mode, but every 25 turns starting with the 27th turn,
592+ re-evaluate the mode. Enter defect mode if any of the following
593+ conditions hold:
594+
595+ - Detected random: Opponent cooperated 7-18 times since last mode
596+ evaluation (or start) AND less than 70% of opponent cooperation was in
597+ response to player's cooperation, i.e.
598+ cc_count / (cc_count+cd_count) < 0.7
599+ - Detect defective: Opponent cooperated fewer than 3 times since last mode
600+ evaluation.
601+
602+ When switching to defect mode, defect immediately. The first two rules for
603+ normal mode require that last three turns were in normal mode. When starting
604+ normal mode from defect mode, defect on first move.
605+
606+ Names:
607+
608+ - Borufsen: [Axelrod1980b]_
609+ """
610+
611+ name = "Borufsen"
612+ classifier = {
613+ 'memory_depth' : float ('inf' ),
614+ 'stochastic' : False ,
615+ 'makes_use_of' : set (),
616+ 'long_run_time' : False ,
617+ 'inspects_source' : False ,
618+ 'manipulates_source' : False ,
619+ 'manipulates_state' : False
620+ }
621+
622+ def __init__ (self ):
623+ super ().__init__ ()
624+ self .cd_counts , self .cc_counts = 0 , 0
625+ self .mutual_defect_streak = 0
626+ self .echo_streak = 0
627+ self .flip_next_defect = False
628+ self .mode = "Normal"
629+
630+ def try_return (self , to_return ):
631+ """
632+ We put the logic here to check for the `flip_next_defect` bit here,
633+ and proceed like normal otherwise.
634+ """
635+
636+ if to_return == C :
637+ return C
638+ # Otherwise look for flip bit.
639+ if self .flip_next_defect :
640+ self .flip_next_defect = False
641+ return C
642+ return D
643+
644+ def strategy (self , opponent : Player ) -> Action :
645+ turn = len (self .history ) + 1
646+
647+ if turn == 1 :
648+ return C
649+
650+ # Update the response history.
651+ if turn >= 3 :
652+ if opponent .history [- 1 ] == C :
653+ if self .history [- 2 ] == C :
654+ self .cc_counts += 1
655+ else :
656+ self .cd_counts += 1
657+
658+ # Check if it's time for a mode change.
659+ if turn > 2 and turn % 25 == 2 :
660+ coming_from_defect = False
661+ if self .mode == "Defect" :
662+ coming_from_defect = True
663+
664+ self .mode = "Normal"
665+ coops = self .cd_counts + self .cc_counts
666+
667+ # Check for a defective strategy
668+ if coops < 3 :
669+ self .mode = "Defect"
670+
671+ # Check for a random strategy
672+ if (coops >= 8 and coops <= 17 ) and self .cc_counts / coops < 0.7 :
673+ self .mode = "Defect"
674+
675+ self .cd_counts , self .cc_counts = 0 , 0
676+
677+ # If defect mode, clear flags
678+ if self .mode == "Defect" :
679+ self .mutual_defect_streak = 0
680+ self .echo_streak = 0
681+ self .flip_next_defect = False
682+
683+ # Check this special case
684+ if self .mode == "Normal" and coming_from_defect :
685+ return D
686+
687+ # Proceed
688+ if self .mode == "Defect" :
689+ return D
690+ else :
691+ assert self .mode == "Normal"
692+
693+ # Look for mutual defects
694+ if self .history [- 1 ] == D and opponent .history [- 1 ] == D :
695+ self .mutual_defect_streak += 1
696+ else :
697+ self .mutual_defect_streak = 0
698+ if self .mutual_defect_streak >= 3 :
699+ self .mutual_defect_streak = 0
700+ self .echo_streak = 0 # Reset both streaks.
701+ return self .try_return (C )
702+
703+ # Look for echoes
704+ # Fortran code defaults two turns back to C if only second turn
705+ my_two_back , opp_two_back = C , C
706+ if turn >= 3 :
707+ my_two_back = self .history [- 2 ]
708+ opp_two_back = opponent .history [- 2 ]
709+ if self .history [- 1 ] != opponent .history [- 1 ] and \
710+ self .history [- 1 ] == opp_two_back and opponent .history [- 1 ] == my_two_back :
711+ self .echo_streak += 1
712+ else :
713+ self .echo_streak = 0
714+ if self .echo_streak >= 3 :
715+ self .mutual_defect_streak = 0 # Reset both streaks.
716+ self .echo_streak = 0
717+ self .flip_next_defect = True
718+
719+ # Tit-for-tat
720+ return self .try_return (opponent .history [- 1 ])
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