Standalone Python 3 scripts for counting various preferential voting elections, including:

• Wright STV
• Single Transferable Vote (weighted inclusive Gregory)
• Instant Runoff Voting (aka. the Alternative Vote)

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./irv.py election.blt

Takes as input an OpenSTV blt file, and calculates the winner under IRV.

Supply the --npr option to use non-proportional representation, iteratively removing the winner from each round to produce an ordered list of winners – as for the filling of casual vacancies.

./stv.py election.blt
./wright_stv.py election.blt

Takes as input an OpenSTV blt file, and calculates the winners under STV/Wright STV.

These scripts can be used to perform a Hare-Clark-style countback to fill vacancies. Firstly, we must capture the quota of votes used to finally elect the candidate causing the vacancy:

./wright_stv.py election.blt --countback CandidateName countback.blt

This command will output a new blt file containing only this quota of votes. We can then run an instant-runoff election with these votes.

./irv.py countback.blt

If some candidates have chosen not to contest the countback, you can add an -ID line into the blt file in the withdrawn candidates block, where ID is the 1-indexed position of the candidate in the candidate list.

On an HP Pavilion dv7-6108tx, the 49,702-vote EVE Online CSM8 election is processed by the EVE Online reference implementation of Wright STV in an average of 6.37 seconds. (±0.04s) The same election is processed by pyRCV's equivalent wright_stv.py --fast --float --noround in an average of 2.34 seconds! (±0.02s) For comparison, using increased-accuracy rational arithmetic (omitting --float) takes an average of 8.64 seconds. (±0.04s)