STVPoll 0.4.1

Example

Case from: https://en.wikipedia.org/wiki/Single_transferable_vote

from stvpoll.scottish_stv import ScottishSTV

example_ballots = (
    (['orange'], 4),
    (['pear', 'orange'], 2),
    (['chocolate', 'strawberry'], 8),
    (['chocolate', 'bonbon'], 4),
    (['strawberry'], 1),
    (['bonbon'], 1),
)

poll = ScottishSTV(seats=3, candidates=['orange', 'chocolate', 'pear', 'strawberry', 'bonbon'])
for (candidates, count) in example_ballots:
    poll.add_ballot(candidates, count)

result = poll.calculate()

This will return a ElectionResult object that contains the result and some useful metadata. The elected attribute contains the elected candidates.

Candidates to the left have higher preference, so: [‘pear’, ‘orange’] means ‘pear’ before ‘orange’ etc. The number is how many of that kind of ballot there is.

result.elected_as_tuple()
('chocolate', 'orange', 'strawberry')

Code & Contributions

You may fork the code at: https://github.com/VoteIT/STVPoll

Please report any bugs there, or email info@voteit.se

0.4.1 (2023-03-09)

Important breaking changes: Result data structure is updated. Import paths changed.

• Rewritten type annotations.

• Rewritten internal data structures, minimizing mutation of data.

• Introducing tiebreak strategies.

• Random tiebreaks not uses a shuffled candidate list, which is reported as part of result.

• Utility to recalculate result from previous polls, using ordered candidate list in randomized tiebreaks.

• STVPollBase class moved from __init__.py to abcs.py.

• Updated result data structure.

0.3.0 (dev)

• Introduce pedantic_order=False, to avoid incomplete results when randomization can not affect who is elected.

0.2.3 (dev)

• Fixed bug where votes were discarded in select_multiple.

• Scottish STV: Select proposals in order of most votes, when there is no more competition.

0.2.2 (dev)

• Fixed bug with tie in first round on Scottish STV.

• Fixed bug in quota selection of all seats in CPO.

0.2.1 (dev)

• Unreleased

0.2.0 (2018-05-23)

• Fixed bug in deciding which vote to transfer first when multiple elected in Scottish STV. [schyffel] [robinharms]

• Scottish STV: Resolve ties so that winners are always in correct ranking order (extreme case). [schyffel]

• Now works on Python 3. [schyffel]

• Test coverage 100 %. [schyffel]

0.1.4 (2018-05-12)

• Fixed a situation where primary_candidate in rounds didn’t exist. [schyffel] [robinharms]

0.1.3 (2018-03-22)

• Excluded empty ballots, so that they do not affect the quota. [schyffel]

0.1.2 (2017-11-24)

• Fixed exception on empty ballots. [schyffel]

0.1.1 (2017-11-24)

• Fixed case where randomization caused an exception. [schyffel]

0.1.0 (2017-11-03)

• Initial version