RuleIRV¶

class whalrus.RuleIRV(*args, base_rule: whalrus.rules.rule.Rule = None, elimination: whalrus.eliminations.elimination.Elimination = None, **kwargs)[source]¶

Instant-Runoff Voting, also known as Alternative Vote, Single Transferable Vote, etc.

Parameters

args – Cf. parent class.
base_rule (Rule) – Default: RulePlurality.
elimination (Elimination) – Default: EliminationLast with k=1.
kwargs – Cf. parent class.

Examples

At each round, the candidate with the worst Plurality score is eliminated.

>>> rule = RuleIRV(['a > b > c', 'b > a > c', 'c > a > b'], weights=[2, 3, 4])
>>> rule.eliminations_[0].rule_.gross_scores_
{'a': 2, 'b': 3, 'c': 4}
>>> rule.eliminations_[1].rule_.gross_scores_
{'b': 5, 'c': 4}
>>> rule.eliminations_[2].rule_.gross_scores_
{'b': 9}
>>> rule.winner_
'b'

An example using the tie-break:

>>> rule = RuleIRV(['a > c > b', 'b > a > c', 'c > a > b'], weights=[1, 2, 1],
...                tie_break=Priority.ASCENDING)
>>> rule.eliminations_[0].rule_.gross_scores_
{'a': 1, 'b': 2, 'c': 1}
>>> rule.eliminations_[1].rule_.gross_scores_
{'a': 2, 'b': 2}
>>> rule.eliminations_[2].rule_.gross_scores_
{'a': 4}
>>> rule.winner_
'a'

property cotrailers_¶

“Cotrailers” of the election, i.e. the candidates that fare worst in the election. This is the last equivalence class in order_. For example, in RuleScoreNum, it is the candidates that are tied for the worst score.

Type: NiceSet

property cowinners_¶

Cowinners of the election, i.e. the candidates that fare best in the election.. This is the first equivalence class in order_. For example, in RuleScoreNum, it is the candidates that are tied for the best score.

Type: NiceSet

property eliminations_¶

The elimination rounds. A list of Elimination objects. The first one corresponds to the first round, etc.

Type: list

property n_candidates_¶

Number of candidates.

Type: int

property strict_order_¶

Result of the election as a strict order over the candidates. The first element is the winner, etc. This may use the tie-breaking rule.

Type: list

property trailer_¶

The “trailer” of the election. This is the last candidate in strict_order_ and also the unfavorable choice of the tie-breaking rule in cotrailers_.

Type: object

property winner_¶

The winner of the election. This is the first candidate in strict_order_ and also the choice of the tie-breaking rule in cowinners_.

Type: object