99 lines
3.8 KiB
Python
99 lines
3.8 KiB
Python
# pyRCV2: Preferential vote counting
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# Copyright © 2020–2021 Lee Yingtong Li (RunasSudo)
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Affero General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Affero General Public License for more details.
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#
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# You should have received a copy of the GNU Affero General Public License
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# along with this program. If not, see <https://www.gnu.org/licenses/>.
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import pytest
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import pyRCV2.blt
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import pyRCV2.numbers
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from pyRCV2.method.base_stv import STVException
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from pyRCV2.method.meek import MeekSTVCounter
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from pyRCV2.model import CandidateState, CountCompleted
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from pyRCV2.ties import TiesBackwards
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def test_meekm_py():
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"""Compare count of meekm.blt with model result produced by Hill et al. reference implementation"""
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pyRCV2.numbers.set_numclass(pyRCV2.numbers.FixedGuarded)
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pyRCV2.numbers.set_dps(4)
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with open('tests/data/meekm.blt', 'r') as f:
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election = pyRCV2.blt.readBLT(f.read())
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assert len(election.candidates) == 4
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cand_a = next(c for c in election.candidates if c.name == 'Adam')
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cand_b = next(c for c in election.candidates if c.name == 'Basil')
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cand_c = next(c for c in election.candidates if c.name == 'Charlotte')
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cand_d = next(c for c in election.candidates if c.name == 'Donald')
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assert election.withdrawn == [cand_b]
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counter = MeekSTVCounter(election, {
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'quota': 'droop_exact',
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'quota_criterion': 'gt',
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'quota_mode': 'progressive',
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'ties': []
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})
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# Stage 1
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result = counter.reset()
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assert result.comment == 'First preferences'
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assert result.total == pyRCV2.numbers.Num('13')
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assert result.quota == pyRCV2.numbers.Num('4')
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assert len(result.candidates.impl) == 4
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assert result.candidates[cand_a].state == CandidateState.ELECTED
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assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
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assert result.candidates[cand_c].state == CandidateState.HOPEFUL
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assert result.candidates[cand_d].state == CandidateState.HOPEFUL
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assert result.candidates[cand_a].votes == pyRCV2.numbers.Num('7')
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assert result.candidates[cand_c].votes == pyRCV2.numbers.Num('1')
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assert result.candidates[cand_d].votes == pyRCV2.numbers.Num('4')
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assert result.exhausted.votes == pyRCV2.numbers.Num('1')
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# Stage 2
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result = counter.step()
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assert result.total == pyRCV2.numbers.Num('13')
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assert result.quota == pyRCV2.numbers.Num('4')
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assert result.candidates[cand_a].state == CandidateState.ELECTED
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assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
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assert result.candidates[cand_c].state == CandidateState.HOPEFUL
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assert result.candidates[cand_d].state == CandidateState.HOPEFUL
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assert result.candidates[cand_a].votes == pyRCV2.numbers.Num('4')
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assert result.candidates[cand_c].votes == pyRCV2.numbers.Num('4')
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assert result.candidates[cand_d].votes == pyRCV2.numbers.Num('4')
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assert result.exhausted.votes == pyRCV2.numbers.Num('1')
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# Stage 3
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# FIXME: This fails in Javascript (rounding errors?)
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with pytest.raises(STVException) as exc_info:
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result = counter.step()
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assert exc_info.value.message == 'Unable to resolve tie'
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# Retry further stages
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counter.options['ties'] = [TiesBackwards(counter)]
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result = counter.step()
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while not isinstance(result, CountCompleted):
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result = counter.step()
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assert result.candidates[cand_a].state == CandidateState.ELECTED
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assert result.candidates[cand_b].state == CandidateState.WITHDRAWN
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assert result.candidates[cand_c].state == CandidateState.EXCLUDED # Charlotte loses the tie if broken backwards
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assert result.candidates[cand_d].state == CandidateState.ELECTED
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