implement single transferable vote

.gitignore

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+secrets.env
+venv

create_secrets.sh

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+#!/bin/sh
+echo "BEARER=???" > secrets.env
+echo "API_VOTE=https://voting.2021.egoi.ch/api/votes/{question_id}" >> secrets.env

requirements.txt

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+python-dotenv
+requests

vote.py

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+#!/usr/bin/env python3
+
+import argparse
+import csv
+import requests
+import os
+
+from io import StringIO
+
+from dotenv import load_dotenv
+
+def get_votes(ids):
+    votes = {}
+    for id in ids:
+        res = requests.get(os.environ['API_VOTE'].format(question_id=id), headers={'Authorization': 'Bearer ' + os.environ['BEARER']})
+        if not res.ok:
+            print('Could not get votes for id', id)
+            continue
+        f = StringIO(res.text)
+        reader = csv.DictReader(f)
+        for row in reader:
+            votes.setdefault(row['Delegation'], []).append(row['Option'])
+    return list(votes.values())
+
+def get_candidates_from_votes(votes):
+    candidates = set()
+    for vote in votes:
+        for option in vote:
+            candidates.add(option)
+    return candidates
+
+def determine_winners(people, votes):
+    """Single Transferable Vote (https://en.wikipedia.org/wiki/Single_transferable_vote)"""
+    elected = []
+    elected_set = set()
+    candidates = get_candidates_from_votes(votes)
+    surplus_votes = {x: 0 for x in candidates}
+    quota = len(votes) / people + 1
+
+    print('Votes:', len(votes))
+    print('Quota:', quota)
+    print('Candidates:', len(candidates))
+
+    def one_round():
+        print('-----------')
+        print('Start Round')
+        print('-----------')
+        round_votes = {x: 0 for x in candidates}
+        for vote in votes:
+            vote_weight = 1
+            for option in vote:
+                if option in elected_set:
+                    vote_weight *= surplus_votes[option]
+                if option in candidates and option not in elected_set:
+                    round_votes[option] += vote_weight
+                    break
+        vote_counts = []
+        for candidate in candidates:
+            if candidate in elected_set:
+                continue
+            vote_counts.append((round_votes[candidate], candidate))
+        vote_counts.sort()
+        print('Vote counts:')
+        for (count, candidate) in reversed(vote_counts):
+            print('  {}: {}'.format(candidate, count))
+        if vote_counts[-1][0] >= quota or len(candidates) == people:
+            elected.append((vote_counts[-1][1], vote_counts[-1][0]))
+            elected_set.add(vote_counts[-1][1])
+
+            surplus = vote_counts[-1][0] - quota
+            if surplus > 0:
+                surplus_votes[vote_counts[-1][1]] = surplus / vote_counts[-1][0]
+
+            print('Elect', vote_counts[-1][1])
+        elif len(candidates) > people:
+            candidates.remove(vote_counts[0][1])
+            print('Remove', vote_counts[0][1])
+
+    while len(elected_set) < people:
+        one_round()
+
+    return elected
+
+def test_votes():
+    return [
+        ['O'],
+        ['O'],
+        ['O'],
+        ['O'],
+        ['P', 'O'],
+        ['P', 'O'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'S'],
+        ['C', 'H'],
+        ['C', 'H'],
+        ['C', 'H'],
+        ['C', 'H'],
+        ['S'],
+        ['H'],
+    ]
+
+def main():
+    load_dotenv('secrets.env')
+    parser = argparse.ArgumentParser(description='Determine voted persons from list of votes.')
+    parser.add_argument('--test', action='store_true', help='Use test values for the votes')
+    parser.add_argument('people', type=int, help='Number of people who need to be voted.')
+    parser.add_argument('questions', type=int, nargs='+', help='IDs of the questions.')
+    args = parser.parse_args()
+    if args.test:
+        votes = test_votes()
+    else:
+        votes = get_votes(args.questions)
+    winners = determine_winners(args.people, votes)
+
+    print('-------------')
+    print('Final results')
+    print('-------------')
+    for i, (winner, votes) in enumerate(winners):
+        print('{:2} with {:2} votes: {}'.format(i+1, int(votes), winner))
+
+if __name__ == '__main__':
+    main()