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STV polling methods

Project description

STVPoll README

https://travis-ci.org/VoteIT/STVPoll.svg?branch=master

Library to perform STV Poll calculations. The package was created as part of the VoteIT project, specifically to handle larger elections that was hard to count with Markus Schulzes STV method.

Typical usage would be primary elections or elections with many winners from a pool of many candidates. The result will be proportional.

Fully supported:

  • Scottish STV

Work in progress:

  • CPO STV

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, bcount) in example_ballots:
    poll.add_ballot(candidates, bcount)

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
[<Candidate: chocolate>, <Candidate: orange>, <Candidate: strawberry>]

Code & Contributions

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

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

Changes

0.2.0 (dev)

  • 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

Project details


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