Package: pyrankvote
PyRankVote —A Ranked Choice Voting System for PythonPyRankVote is a python library for different ranked-choice voting systems (sometimes called preferential voting systems) created by Jon Tingvold in June 2019.The following ranking methods are implemented for electing one person/alternative (e.g. electing the chairman to a board):Instant-runoff voting (IRV)—often known as the alternative voteThe following ranking methods are implemented for electing multiple people/alternatives (e.g. electing board members):Single transferable vote (STV)—generally preferredPreferential block voting (PBV)Different ranking methodsInstant runoff voting (IRV)is a single candidate election method that elects the candidate that can obtain majority support (more than 50%).Voters rank candidates and are granted one vote. The candidate with fewest votes is removed and this candidate's votes are transferred according to the voters 2nd preference (or 3rd etc).Preferential block voting (PBV)is a multiple candidate election method that elects candidates that
can obtain majority support (more than 50%). PBV tends to elect uncontroversial candidates that agree with each other. Minority group often lose their representation.Voters rank candidates and are granted as many votes as there are people that should be elected. The candidate with
fewest votes are removed and this candidate's votes are transferred according to the voters 2nd preference (or 3rd etc).Single transferable vote (STV)is a multiple candidate election method that elects candidates based on proportional representation. Minority (and extreme) groups get representation if they have enough votes to elect a candidate. STV is therefore the preferred ranked-choice voting method for parliament elections and most multiple seat elections, but it's more complex than PBV, so it explained last.Voters rank candidates and are granted as one vote each. If a candidate gets more votes than the threshold for being
elected, the candidate is proclaimed as winner. This function uses the Droop quota, wheredroop_quota=votes/(seats+1)+1If one candidate gets more votes than the threshold the excess votes are transferred to voters that voted for this
candidate's 2nd (or 3rd, 4th, etc) alternative. If no candidate gets over the threshold, the candidate with fewest votes
is removed. Votes for this candidate is then transferred to voters 2nd (or 3rd, 4th, etc) alternative.Preferential block voting and Single transferable vote are the same as Instant-runoff voting when only one candidate is elected.Instant-runoff voting and Preferential block voting are basically the same asexhaustive ballot, the preferred method in Rober's rules of order. The only difference is that in exhaustive ballot voters can adjust their preferences between each round (elimination or election of one candidate).For more info:pyrankvote/single_seat_ranking_methods.pyandpyrankvote/multiple_seat_ranking_methods.pyWikipedia:IRV,STV,PBV,exhaustive ballotCGP Gray's YouTube videos:IRV,STV1,STV2,STV3InstallationWith pip package manager:pipinstallpyrankvoteUsageimportpyrankvotefrompyrankvoteimportCandidate,Ballotbush=Candidate("George W. Bush (Republican)")gore=Candidate("Al Gore (Democratic)")nader=Candidate("Ralph Nader (Green)")candidates=[bush,gore,nader]# Bush have most first choice votes, but because Ralph Nader-voters want# Al Gore if Nader is not elected, the elected candidate is Al Goreballots=[Ballot(ranked_candidates=[bush,nader,gore]),Ballot(ranked_candidates=[bush,nader,gore]),Ballot(ranked_candidates=[bush,nader]),Ballot(ranked_candidates=[bush,nader]),Ballot(ranked_candidates=[nader,gore,bush]),Ballot(ranked_candidates=[nader,gore]),Ballot(ranked_candidates=[gore,nader,bush]),Ballot(ranked_candidates=[gore,nader]),Ballot(ranked_candidates=[gore,nader])]# You can use your own Candidate and Ballot objects as long as they implement the same properties and methodselection_result=pyrankvote.instant_runoff_voting(candidates,ballots)winners=election_result.get_winners()# Returns: [<Candidate('Al Gore (Democratic)')>]print(election_result)# Prints:"""ROUND 1Candidate                      Votes  Status---------------------------  -------  --------George W. Bush (Republican)        4  HopefulAl Gore (Democratic)               3  HopefulRalph Nader (Green)                2  RejectedFINAL RESULTCandidate                      Votes  Status---------------------------  -------  --------Al Gore (Democratic)               5  ElectedGeorge W. Bush (Republican)        4  RejectedRalph Nader (Green)                0  Rejected"""More examples inexamples.pyVersionsv2.0.6 (2022-10-15) Fix compatibility with new tabular version under Python 3.10v2.0 (2020-04-08):Compact round results and standard STV-procedureNon-backward compatible change: If ballot exhausted, the ballot is now thrown away instead of picking a candidate at random. This is more in line with most RCV-systems. The old practice can be reenabled withpyrankvote.single_transferable_vote(candidates, ballots, pick_random_if_blank=True)v1.0 (2019-09-15):Stable release.First release I assume is stable enough to encourage use.v0.0 (2019-08-09):Pre-releasePopularityCurrently (summer 2022) the library is downloaded round 300 times per month from PyPi (pip). That figure does not include downloads that look like they are coming from bots/mirrors/grab scripts.ContributingPull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.Please make sure to update tests as appropriate.Questions?Feel free tosend me an emailif you have questions about the project.LicenseMIT