Build new types of tournamentsΒΆ

It is possible to create new tournaments not yet implemented in the library itself. There are two tools that make up a tournament:

  • The MatchGenerator class: this class is responsible for generating the required matches.
  • The Tournament class: this class is responsible for playing the matches generated.

Let us aim to create a round robin tournament of matches with 5 turns each with the modification that two players only play each other with .5 probability.

To do this let us create a new class to generate matches:

>>> import axelrod as axl
>>> import random
>>> axl.seed(0)  # Setting a seed.
>>> class StochasticMatchups(axl.RoundRobinMatches):
...     """Inherit from the `axelrod.match_generator.RoundRobinMatches` class"""
...
...     def build_match_chunks(self):
...         """
...         A generator that yields match parameters only with a given probability.
...
...         This over writes the
...         `axelrod.match_generator.RoundRobinMatches.build_match_chunks` method.
...         """
...         for player1_index in range(len(self.players)):
...             for player2_index in range(player1_index, len(self.players)):
...                 if random.random() < 0.5:  # This is the modification
...                     match_params = self.build_single_match_params()
...                     index_pair = (player1_index, player2_index)
...                     yield (index_pair, match_params, self.repetitions)

Using this class we can create a tournament with little effort:

>>> players = [axl.Cooperator(), axl.Defector(), axl.TitForTat(),
...            axl.Grudger(), axl.Alternator()]
>>> tournament = axl.Tournament(players, match_generator=StochasticMatchups, turns=2, repetitions=2)
>>> results = tournament.play(keep_interactions=True)

We can then look at the interactions (results may differ based on random seed) for the first repetition:

>>> for index_pair, interaction in results.interactions.items():
...     player1 = tournament.players[index_pair[0]]
...     player2 = tournament.players[index_pair[1]]
...     print('%s vs %s: %s' % (player1, player2, interaction))  
Cooperator vs Defector: [[('C', 'D'), ('C', 'D')], [('C', 'D'), ('C', 'D')]]
Alternator vs Alternator: [[('C', 'C'), ('D', 'D')], [('C', 'C'), ('D', 'D')]]
Tit For Tat vs Grudger: [[('C', 'C'), ('C', 'C')], [('C', 'C'), ('C', 'C')]]
Grudger vs Grudger: [[('C', 'C'), ('C', 'C')], [('C', 'C'), ('C', 'C')]]
Tit For Tat vs Tit For Tat: [[('C', 'C'), ('C', 'C')], [('C', 'C'), ('C', 'C')]]
Cooperator vs Alternator: [[('C', 'C'), ('C', 'D')], [('C', 'C'), ('C', 'D')]]
Defector vs Defector: [[('D', 'D'), ('D', 'D')], [('D', 'D'), ('D', 'D')]]

We see that not all possible matches were played (for example Cooperator has not played TitForTat). The results can be viewed as before:

>>> results.ranked_names
['Cooperator', 'Defector', 'Tit For Tat', 'Grudger', 'Alternator']

Note: the axelrod.MatchGenerator also has a build_single_match method which can be overwritten (similarly to above) if the type of a particular match should be changed.

For example the following could be used to create a tournament that randomly builds matches that were either 200 turns or single 1 shot games:

>>> class OneShotOrRepetitionMatchups(axl.RoundRobinMatches):
...     """Inherit from the `axelrod.match_generator.RoundRobinMatches` class"""
...
...
...     def build_single_match_params(self):
...         """Create a single set of match parameters"""
...         turns = 1
...         if random.random() < 0.5:
...             turns = 200
...         return (turns, self.game, None, self.noise)

We can take a look at the match lengths when using this generator:

>>> players = [axl.Cooperator(), axl.Defector(), axl.TitForTat(),
...            axl.Grudger(), axl.Alternator()]
>>> tournament = axl.Tournament(players, match_generator=OneShotOrRepetitionMatchups,
...                             turns=float("inf"), repetitions=1)
>>> results = tournament.play(keep_interactions=True)
>>> sorted(list(set([len(matches[0]) for matches in results.interactions.values()])))
[1, 200]