kopia lustrzana https://github.com/martinlackner/apportionment
possible to raise exceptions when ties occur
Martin Lackner
rodzic
f92f07b46a
commit
e29a7e74b3
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@ -7,19 +7,29 @@ import math
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from fractions import Fraction
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METHODS = ["quota", "largest_remainder", "dhondt", "saintelague",
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"modified_saintelague", "huntington", "adams", "dean"]
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class TiesException(Exception):
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pass
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def compute(method, votes, seats, parties=string.ascii_letters,
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threshold=None, verbose=True):
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threshold=None, tiesallowed=True, verbose=True):
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filtered_votes = apply_threshold(votes, threshold)
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if method == "quota":
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return quota(filtered_votes, seats, parties, verbose)
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return quota(filtered_votes, seats, parties, tiesallowed, verbose)
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elif method in ["lrm", "hamilton", "largest_remainder"]:
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return largest_remainder(filtered_votes, seats, parties, verbose)
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return largest_remainder(filtered_votes, seats, parties,
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tiesallowed, verbose)
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elif method in ["dhondt", "jefferson", "saintelague", "webster",
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"modified_saintelague",
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"huntington", "hill", "adams", "dean",
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"smallestdivisor", "harmonicmean", "equalproportions",
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"majorfractions", "greatestdivisors"]:
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return divisor(filtered_votes, seats, method, parties, verbose)
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return divisor(filtered_votes, seats, method, parties,
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tiesallowed, verbose)
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else:
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raise NotImplementedError("apportionment method " + method +
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" not known")
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@ -73,19 +83,20 @@ def within_quota(votes, representatives, parties=string.ascii_letters,
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# Largest remainder method (Hamilton method)
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def largest_remainder(votes, seats, parties=string.ascii_letters,
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verbose=True):
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tiesallowed=True, verbose=True):
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if verbose:
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print("\nLargest remainder method with Hare quota (Hamilton)")
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q = Fraction(sum(votes), seats)
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quotas = [Fraction(p, q) for p in votes]
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representatives = [int(qu.numerator)//int(qu.denominator) for qu in quotas]
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ties = False
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if sum(representatives) < seats:
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remainders = [a-b for a, b in zip(quotas, representatives)]
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cutoff = sorted(remainders, reverse=True)[seats-sum(representatives)-1]
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tiebreaking_message = (" tiebreaking in order of: " +
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str(parties[:len(votes)]) +
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"\n ties broken in favor of: ")
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ties = False
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for i in range(len(votes)):
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if sum(representatives) == seats and remainders[i] >= cutoff:
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if not ties:
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@ -101,6 +112,9 @@ def largest_remainder(votes, seats, parties=string.ascii_letters,
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if ties and verbose:
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print(tiebreaking_message[:-2])
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if ties and not tiesallowed:
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raise TiesException("Tie occurred")
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if verbose:
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__print_results(representatives, parties)
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@ -109,7 +123,7 @@ def largest_remainder(votes, seats, parties=string.ascii_letters,
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# Divisor methods
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def divisor(votes, seats, method, parties=string.ascii_letters,
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verbose=True):
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tiesallowed=True, verbose=True):
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representatives = [0] * len(votes)
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if method in ["dhondt", "jefferson", "greatestdivisors"]:
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if verbose:
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@ -127,9 +141,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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if verbose:
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print("\nHuntington-Hill method")
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if seats < len(votes):
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representatives = __divzero_fewerseatsthanparties(votes,
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seats, parties,
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verbose)
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representatives = __divzero_fewerseatsthanparties(
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votes, seats, parties, tiesallowed, verbose)
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else:
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representatives = [1 if p > 0 else 0 for p in votes]
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divisors = [math.sqrt((i+1)*(i+2)) for i in range(seats)]
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@ -137,9 +150,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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if verbose:
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print("\nAdams method")
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if seats < len(votes):
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representatives = __divzero_fewerseatsthanparties(votes,
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seats, parties,
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verbose)
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representatives = __divzero_fewerseatsthanparties(
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votes, seats, parties, tiesallowed, verbose)
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else:
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representatives = [1 if p > 0 else 0 for p in votes]
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divisors = [i+1 for i in range(seats)]
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@ -147,9 +159,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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if verbose:
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print("\nDean method")
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if seats < len(votes):
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representatives = __divzero_fewerseatsthanparties(votes,
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seats, parties,
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verbose)
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representatives = __divzero_fewerseatsthanparties(
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votes, seats, parties, tiesallowed, verbose)
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else:
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representatives = [1 if p > 0 else 0 for p in votes]
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divisors = [Fraction(2 * (i+1) * (i+2), 2 * (i+1) + 1)
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@ -180,6 +191,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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for i in range(len(votes)):
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if sum(representatives) == seats and minweight in weights[i]:
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if not ties:
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if not tiesallowed:
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raise TiesException("Tie occurred")
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tiebreaking_message = tiebreaking_message[:-2]
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tiebreaking_message += "\n to the disadvantage of: "
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ties = True
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@ -190,6 +203,9 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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if ties and verbose:
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print(tiebreaking_message[:-2])
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if ties and not tiesallowed:
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raise TiesException("Tie occurred")
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if verbose:
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__print_results(representatives, parties)
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@ -197,7 +213,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
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# required for methods with 0 divisors (Adams, Huntington-Hill)
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def __divzero_fewerseatsthanparties(votes, seats, parties, verbose):
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def __divzero_fewerseatsthanparties(votes, seats, parties,
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tiesallowed, verbose):
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representatives = [0] * len(votes)
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if verbose:
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print(" fewer seats than parties; " + str(seats) +
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@ -216,6 +233,8 @@ def __divzero_fewerseatsthanparties(votes, seats, parties, verbose):
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tiebreaking_message += "\n to the disadvantage of: "
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ties = True
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tiebreaking_message += parties[i] + ", "
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if ties and not tiesallowed:
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raise TiesException("Tie occurred")
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if ties and verbose:
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print(tiebreaking_message[:-2])
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return representatives
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@ -225,43 +244,50 @@ def __divzero_fewerseatsthanparties(votes, seats, parties, verbose):
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# ( see Balinski, M. L., & Young, H. P. (1975).
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# The quota method of apportionment.
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# The American Mathematical Monthly, 82(7), 701-730.)
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def quota(votes, seats, parties=string.ascii_letters, verbose=True):
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def quota(votes, seats, parties=string.ascii_letters,
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tiesallowed=True, verbose=True):
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if verbose:
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print("\nQuota method")
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representatives = [0] * len(votes)
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tied = []
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for k in range(1, seats+1):
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while sum(representatives) < seats:
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quotas = [Fraction(votes[i], representatives[i]+1)
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for i in range(len(votes))]
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# check if upper quota is violated
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for i in range(len(votes)):
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upperquota = int(math.ceil(float(votes[i]) *
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k / sum(votes)))
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(sum(representatives)+1)
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/ sum(votes)))
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if representatives[i] >= upperquota:
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quotas[i] = 0
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chosen = [i for i in range(len(votes))
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if quotas[i] == max(quotas)]
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if verbose:
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if len(chosen) > 1:
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tied.append(representatives[chosen[0]])
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else:
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tied = []
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representatives[chosen[0]] += 1
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maxquotas = [i for i in range(len(votes))
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if quotas[i] == max(quotas)]
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nextrep = maxquotas[0]
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representatives[nextrep] += 1
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if len(maxquotas) > 1 and not tiesallowed:
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raise TiesException("Tie occurred")
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# print tiebreaking information
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if verbose and len(tied) > 0:
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if verbose and len(maxquotas) > 1:
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quotas_now = [Fraction(votes[i], representatives[i]+1)
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for i in range(len(votes))]
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tiebreaking_message = (" tiebreaking in order of: " +
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str(parties[:len(votes)]) +
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"\n ties broken in favor of: ")
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for i in range(len(tied)):
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tiebreaking_message += tied[i] + ", "
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ties_favor = [i for i in range(len(votes))
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if quotas_now[i] == quotas_now[nextrep]]
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for i in ties_favor:
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tiebreaking_message += str(parties[i]) + ", "
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tiebreaking_message = (tiebreaking_message[:-2] +
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"\n to the disadvantage of: ")
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for i in range(1, len(chosen)):
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tiebreaking_message += tied[i] + ", "
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print(tiebreaking_message)
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for i in maxquotas[1:]:
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tiebreaking_message += str(parties[i]) + ", "
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print(tiebreaking_message[:-2])
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if verbose:
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__print_results(representatives, parties)
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return representatives
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@ -5,10 +5,6 @@ import unittest
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import apportionment.methods as app
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METHODS = ["quota", "largest_remainder", "dhondt", "saintelague",
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"modified_saintelague", "huntington", "adams", "dean"]
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class TestApprovalMultiwinner(unittest.TestCase):
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def test_all_implemented(self):
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@ -32,7 +28,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
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votes = [14, 28, 7, 35]
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seats = 12
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for method in METHODS:
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for method in app.METHODS:
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result = app.compute(method, votes,
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seats, verbose=False)
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self.assertEqual(result, [2, 4, 1, 5],
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@ -43,7 +39,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
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votes = [0, 14, 28, 0, 0]
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seats = 6
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for method in METHODS:
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for method in app.METHODS:
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result = app.compute(method, votes,
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seats, verbose=False)
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self.assertEqual(result, [0, 2, 4, 0, 0],
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@ -54,13 +50,13 @@ class TestApprovalMultiwinner(unittest.TestCase):
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votes = [10, 9, 8, 8, 11, 12]
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seats = 3
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for method in METHODS:
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for method in app.METHODS:
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result = app.compute(method, votes,
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seats, verbose=False)
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self.assertEqual(result, [1, 0, 0, 0, 1, 1],
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msg=method + " failed")
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# example taken from
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# examples taken from
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# Balinski, M. L., & Young, H. P. (1975).
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# The quota method of apportionment.
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# The American Mathematical Monthly, 82(7), 701-730.
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@ -111,7 +107,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
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votes = [2, 1, 1, 2, 2]
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seats = 2
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for method in METHODS:
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for method in app.METHODS:
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result = app.compute(method, votes,
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seats, verbose=False)
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self.assertEqual(result, [1, 0, 0, 1, 0],
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@ -161,8 +157,28 @@ class TestApprovalMultiwinner(unittest.TestCase):
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r2 = app.compute("modified_saintelague", votes,
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seats, verbose=False) # [4, 0]
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self.assertNotEqual(r1, r2,
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"Saintelague and its modified variant"
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+ "should produce differents results.")
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"Sainte Lague and its modified variant"
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+ "should produce different results.")
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def test_no_ties_allowed(self):
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self.longMessage = True
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votes = [11, 11, 11]
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seats = 4
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for method in app.METHODS:
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with self.assertRaises(app.TiesException,
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msg=method + " failed"):
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app.compute(method, votes, seats,
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tiesallowed=False, verbose=False)
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def test_no_ties_allowed2(self):
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self.longMessage = True
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votes = [12, 12, 11, 12]
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seats = 3
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for method in app.METHODS:
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self.assertEqual(
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app.compute(method, votes, seats,
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tiesallowed=False, verbose=False),
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[1, 1, 0, 1], msg=method + " failed")
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if __name__ == '__main__':
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