stv

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from operator import mul, itemgetter

from random import random, seed

import logging

import sys

import math

import csv

import argparse

SVT_LOGGER = 'SVT'

LOGGER_FORMAT = '%(levelname)s %(message)s'

LOG_MESSAGE = "{action} {desc}"

class Action:

    COUNT_ROUND = "@ROUND"

    TRANSFER = ">TRANSFER"

    ELIMINATE = "-ELIMINATE"

    ELECT = "+ELECT"

    COUNT = ".COUNT"

    RANDOM = "*RANDOM"

    THRESHOLD = "^THRESHOLD"

logging.basicConfig(format=LOGGER_FORMAT)

logging.getLogger(SVT_LOGGER).setLevel(logging.INFO)

class Ballot:

    """A ballot class for Single Transferable Voting.

    The ballot class contains an ordered list of candidates (in

    decreasing order of preference) and an ordered list of weights

    (new weights are added to the front of the list). The index of the

    current preference (for the first count and subsequent rounds)

    is also kept.

    """

    candidates = []

    weights = [1.0]

    current_preference = 0

    _value = 1.0

    def __init__(self, candidates=[]):

        self.candidates = candidates

    def add_weight(self, weight):

        self.weights.insert(0, weight)

        self._value *= weight

    def get_value(self):

        return self._value

def random_generator(num):

    if not random_sequence:

        print "Need random from " + num

        sys.exit()

    else:

        return random_sequence.pop(0)

def randomly_select_first(sequence, key, action, random_generator=None):

    """Selects the first item of equals in a sorted sequence of items.

    For the given sorted sequence, returns the first item if it

    is different than the second; if there are ties so that there

    are items with equal values, it randomly selects among those items.

    The value of each item in the sequence is provided by applying the

    function key to the item. The action parameter indicates the context

    in which the random selection takes place (election or elimination).

    random_generator, if given, is the function that produces the random

    selection.

    """

    first_value = key(sequence[0])

    collected = []

    for item in sequence:

        if key(item) == first_value:

            collected.append(item)

        else:

            break

    index = 0

    num_eligibles = len(collected)

    if (num_eligibles > 1):

        if random_generator is None:

            index = int(random() * num_eligibles)

        else:

            index = random_generator(num_eligibles)

        selected = collected[index]

        logger = logging.getLogger(SVT_LOGGER)

        description = "{0} from {1} to {2}".format(selected, collected, action)

        logger.info(LOG_MESSAGE.format(action=Action.RANDOM, desc=description))

    return collected[index]

def redistribute_ballots(selected, hopefuls, allocated, weight, vote_count):

    """Redistributes the ballots from selected to the hopefuls.

    Redistributes the ballots currently allocated to the selected

    candidate. The ballots are redistributed with the given weight.

    The total ballot allocation is given by the allocated dict. The current

    vote count is given by vote_count and is adjusted according to the

    redistribution.

    """

    logger = logging.getLogger(SVT_LOGGER)

    transferred = []

    # Keep a hash of ballot moves for logging purposes.

    # The hash comprises 

    moves = {}

    for ballot in allocated[selected]:

        reallocated = False

        i = ballot.current_preference + 1

        while not reallocated and i < len(ballot.candidates):

            recipient = ballot.candidates[i]

            if recipient in hopefuls:

                ballot.current_preference = i

                ballot.add_weight(weight)

                current_value = ballot.get_value()

                if recipient in allocated:

                    allocated[recipient].append(ballot)

                else:

                    allocated[recipient] = [ballot]

                if recipient in vote_count:

                    vote_count[recipient] += current_value

                else:

                    vote_count[recipient] = current_value

                vote_count[selected] -= current_value

                reallocated = True

                if (selected, recipient, current_value) in moves:

                    moves[(selected, recipient, current_value)] += 1

                else:

                    moves[(selected, recipient, current_value)] = 1

                transferred.append(ballot)

            else:

                i += 1

    for move, times in moves.iteritems():

        description =  "from {0} to {1} {2}*{3}={4}".format(move[0],

                                                            move[1],

                                                            times,

                                                            move[2],

                                                            times*move[2])

        logger.info(LOG_MESSAGE.format(action=Action.TRANSFER,

                                       desc=description))

    allocated[selected][:] = [x for x in allocated[selected]

                              if x not in transferred ]

def count_stv(ballots, seats, rnd_gen=None):

    """Performs a SVT vote for the given ballots and number of seats.

    """

    allocated = {} # The allocation of ballots to candidates

    vote_count = {} # A hash of ballot counts, indexed by candidates

    candidates = [] # All candidates

    elected = [] # The candidates that have been elected

    hopefuls = [] # The candidates that may be elected

    seed()

    threshold = (1 + len(ballots) / (seats + 1))

    logger = logging.getLogger(SVT_LOGGER)

    logger.info(LOG_MESSAGE.format(action=Action.THRESHOLD,

                                   desc=threshold))

    # Do initial count

    for ballot in ballots:

        selected = ballot.candidates[0]

        for candidate in ballot.candidates:

            if candidate not in candidates:

                candidates.append(candidate)

                vote_count[candidate] = 0

        if selected in allocated:

            allocated[selected].append(ballot)

        else:

            allocated[selected] = [ballot]

        vote_count[selected] += 1

    # In the beginning, all candidates are hopefuls

    hopefuls = [x for x in candidates]

    # Start rounds

    current_round = 1

    num_elected = len(elected)

    num_hopefuls = len(hopefuls)

    while num_elected < seats and num_hopefuls > 0:

        logger.info(LOG_MESSAGE.format(action=Action.COUNT_ROUND,

                                       desc=current_round))

        # Log count 

        description  = ';'.join(map(lambda x: "{0} = {1}".format(x,

                                                                 vote_count[x]),

                                    candidates))

        logger.info(LOG_MESSAGE.format(action=Action.COUNT,

                                       desc=description))

        hopefuls_sorted = sorted(hopefuls, key=vote_count.get, reverse=True )

        # If there is a surplus try to redistribute the best candidate's votes

        # according to their next preferences

        surplus = vote_count[hopefuls_sorted[0]] - threshold

        remaining_seats = seats - num_elected

        if surplus >= 0 or num_hopefuls <= remaining_seats:

            best_candidate = randomly_select_first(hopefuls_sorted,

                                                   key=vote_count.get,

                                                   action=Action.ELECT,

                                                   random_generator=rnd_gen)

            hopefuls.remove(best_candidate)

            elected.append(best_candidate)

            logger.info(LOG_MESSAGE.format(action=Action.ELECT,

                                           desc=best_candidate))

            if surplus > 0:

                # Calculate the weight for this round

                weight = float(surplus) / vote_count[best_candidate]

                # Find the next eligible preference for each one of the ballots

                # cast for the candidate, and transfer the vote to that

                # candidate with its value adjusted by the correct weight.

                redistribute_ballots(best_candidate, hopefuls, allocated,

                                     weight, vote_count)

        # If there is no surplus, take the least hopeful candidate

        # (i.e., the hopeful candidate with the less votes) and

        # redistribute that candidate's votes.

        else:

            hopefuls_sorted.reverse()

            worst_candidate = randomly_select_first(hopefuls_sorted,

                                                    key=vote_count.get,

                                                    action=Action.ELIMINATE,

                                                    random_generator=rnd_gen)

            hopefuls.remove(worst_candidate)

            logger.info(LOG_MESSAGE.format(action=Action.ELIMINATE,

                                           desc=worst_candidate))

            redistribute_ballots(worst_candidate, hopefuls, allocated, 1.0,

                                 vote_count)

        current_round += 1

        num_hopefuls = len(hopefuls)

        num_elected = len(elected)

    return elected, vote_count

if __name__ == "__main__":

    parser = argparse.ArgumentParser(description='Perform STV')

    parser.add_argument('--ballots', nargs='?', default='sys.stdin',

                        dest='ballots_file', help='input ballots file')

    parser.add_argument('--seats', nargs='?', default=0,

                        dest='seats', help='number of seats')

    args = parser.parse_args()

    ballots = []

    ballots_file = sys.stdin

    if args.ballots_file != 'sys.stdin':

        ballots_file = open(args.ballots_file)

    ballots_reader = csv.reader(ballots_file, delimiter=',',

                                quotechar='"',

                                skipinitialspace = True)

    for ballot in ballots_reader:

        ballots.append(Ballot(ballot))

    if args.seats == 0:

        args.seats = len(ballots) / 2

    (elected, vote_count) = count_stv(ballots, int(args.seats))

    print "Results:"

    for candidate in elected:

        print candidate, vote_count[candidate]