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possible to raise exceptions when ties occur

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Martin Lackner 2020-02-03 20:23:40 +01:00
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commit e29a7e74b3
2 zmienionych plików z 88 dodań i 46 usunięć
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96
apportionment/methods.py
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@ -7,19 +7,29 @@ import math
from fractions import Fraction from fractions import Fraction
METHODS = ["quota", "largest_remainder", "dhondt", "saintelague",
"modified_saintelague", "huntington", "adams", "dean"]
class TiesException(Exception):
pass
def compute(method, votes, seats, parties=string.ascii_letters, def compute(method, votes, seats, parties=string.ascii_letters,
threshold=None, verbose=True): threshold=None, tiesallowed=True, verbose=True):
filtered_votes = apply_threshold(votes, threshold) filtered_votes = apply_threshold(votes, threshold)
if method == "quota": if method == "quota":
return quota(filtered_votes, seats, parties, verbose) return quota(filtered_votes, seats, parties, tiesallowed, verbose)
elif method in ["lrm", "hamilton", "largest_remainder"]: elif method in ["lrm", "hamilton", "largest_remainder"]:
return largest_remainder(filtered_votes, seats, parties, verbose) return largest_remainder(filtered_votes, seats, parties,
tiesallowed, verbose)
elif method in ["dhondt", "jefferson", "saintelague", "webster", elif method in ["dhondt", "jefferson", "saintelague", "webster",
"modified_saintelague", "modified_saintelague",
"huntington", "hill", "adams", "dean", "huntington", "hill", "adams", "dean",
"smallestdivisor", "harmonicmean", "equalproportions", "smallestdivisor", "harmonicmean", "equalproportions",
"majorfractions", "greatestdivisors"]: "majorfractions", "greatestdivisors"]:
return divisor(filtered_votes, seats, method, parties, verbose) return divisor(filtered_votes, seats, method, parties,
tiesallowed, verbose)
else: else:
raise NotImplementedError("apportionment method " + method + raise NotImplementedError("apportionment method " + method +
" not known") " not known")
@ -73,19 +83,20 @@ def within_quota(votes, representatives, parties=string.ascii_letters,
# Largest remainder method (Hamilton method) # Largest remainder method (Hamilton method)
def largest_remainder(votes, seats, parties=string.ascii_letters, def largest_remainder(votes, seats, parties=string.ascii_letters,
verbose=True): tiesallowed=True, verbose=True):
if verbose: if verbose:
print("\nLargest remainder method with Hare quota (Hamilton)") print("\nLargest remainder method with Hare quota (Hamilton)")
q = Fraction(sum(votes), seats) q = Fraction(sum(votes), seats)
quotas = [Fraction(p, q) for p in votes] quotas = [Fraction(p, q) for p in votes]
representatives = [int(qu.numerator)//int(qu.denominator) for qu in quotas] representatives = [int(qu.numerator)//int(qu.denominator) for qu in quotas]
ties = False
if sum(representatives) < seats: if sum(representatives) < seats:
remainders = [a-b for a, b in zip(quotas, representatives)] remainders = [a-b for a, b in zip(quotas, representatives)]
cutoff = sorted(remainders, reverse=True)[seats-sum(representatives)-1] cutoff = sorted(remainders, reverse=True)[seats-sum(representatives)-1]
tiebreaking_message = (" tiebreaking in order of: " + tiebreaking_message = (" tiebreaking in order of: " +
str(parties[:len(votes)]) + str(parties[:len(votes)]) +
"\n ties broken in favor of: ") "\n ties broken in favor of: ")
ties = False
for i in range(len(votes)): for i in range(len(votes)):
if sum(representatives) == seats and remainders[i] >= cutoff: if sum(representatives) == seats and remainders[i] >= cutoff:
if not ties: if not ties:
@ -101,6 +112,9 @@ def largest_remainder(votes, seats, parties=string.ascii_letters,
if ties and verbose: if ties and verbose:
print(tiebreaking_message[:-2]) print(tiebreaking_message[:-2])
if ties and not tiesallowed:
raise TiesException("Tie occurred")
if verbose: if verbose:
__print_results(representatives, parties) __print_results(representatives, parties)
@ -109,7 +123,7 @@ def largest_remainder(votes, seats, parties=string.ascii_letters,
# Divisor methods # Divisor methods
def divisor(votes, seats, method, parties=string.ascii_letters, def divisor(votes, seats, method, parties=string.ascii_letters,
verbose=True): tiesallowed=True, verbose=True):
representatives = [0] * len(votes) representatives = [0] * len(votes)
if method in ["dhondt", "jefferson", "greatestdivisors"]: if method in ["dhondt", "jefferson", "greatestdivisors"]:
if verbose: if verbose:
@ -127,9 +141,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
if verbose: if verbose:
print("\nHuntington-Hill method") print("\nHuntington-Hill method")
if seats < len(votes): if seats < len(votes):
representatives = __divzero_fewerseatsthanparties(votes, representatives = __divzero_fewerseatsthanparties(
seats, parties, votes, seats, parties, tiesallowed, verbose)
verbose)
else: else:
representatives = [1 if p > 0 else 0 for p in votes] representatives = [1 if p > 0 else 0 for p in votes]
divisors = [math.sqrt((i+1)*(i+2)) for i in range(seats)] divisors = [math.sqrt((i+1)*(i+2)) for i in range(seats)]
@ -137,9 +150,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
if verbose: if verbose:
print("\nAdams method") print("\nAdams method")
if seats < len(votes): if seats < len(votes):
representatives = __divzero_fewerseatsthanparties(votes, representatives = __divzero_fewerseatsthanparties(
seats, parties, votes, seats, parties, tiesallowed, verbose)
verbose)
else: else:
representatives = [1 if p > 0 else 0 for p in votes] representatives = [1 if p > 0 else 0 for p in votes]
divisors = [i+1 for i in range(seats)] divisors = [i+1 for i in range(seats)]
@ -147,9 +159,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
if verbose: if verbose:
print("\nDean method") print("\nDean method")
if seats < len(votes): if seats < len(votes):
representatives = __divzero_fewerseatsthanparties(votes, representatives = __divzero_fewerseatsthanparties(
seats, parties, votes, seats, parties, tiesallowed, verbose)
verbose)
else: else:
representatives = [1 if p > 0 else 0 for p in votes] representatives = [1 if p > 0 else 0 for p in votes]
divisors = [Fraction(2 * (i+1) * (i+2), 2 * (i+1) + 1) divisors = [Fraction(2 * (i+1) * (i+2), 2 * (i+1) + 1)
@ -180,6 +191,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
for i in range(len(votes)): for i in range(len(votes)):
if sum(representatives) == seats and minweight in weights[i]: if sum(representatives) == seats and minweight in weights[i]:
if not ties: if not ties:
if not tiesallowed:
raise TiesException("Tie occurred")
tiebreaking_message = tiebreaking_message[:-2] tiebreaking_message = tiebreaking_message[:-2]
tiebreaking_message += "\n to the disadvantage of: " tiebreaking_message += "\n to the disadvantage of: "
ties = True ties = True
@ -190,6 +203,9 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
if ties and verbose: if ties and verbose:
print(tiebreaking_message[:-2]) print(tiebreaking_message[:-2])
if ties and not tiesallowed:
raise TiesException("Tie occurred")
if verbose: if verbose:
__print_results(representatives, parties) __print_results(representatives, parties)
@ -197,7 +213,8 @@ def divisor(votes, seats, method, parties=string.ascii_letters,
# required for methods with 0 divisors (Adams, Huntington-Hill) # required for methods with 0 divisors (Adams, Huntington-Hill)
def __divzero_fewerseatsthanparties(votes, seats, parties, verbose): def __divzero_fewerseatsthanparties(votes, seats, parties,
tiesallowed, verbose):
representatives = [0] * len(votes) representatives = [0] * len(votes)
if verbose: if verbose:
print(" fewer seats than parties; " + str(seats) + print(" fewer seats than parties; " + str(seats) +
@ -216,6 +233,8 @@ def __divzero_fewerseatsthanparties(votes, seats, parties, verbose):
tiebreaking_message += "\n to the disadvantage of: " tiebreaking_message += "\n to the disadvantage of: "
ties = True ties = True
tiebreaking_message += parties[i] + ", " tiebreaking_message += parties[i] + ", "
if ties and not tiesallowed:
raise TiesException("Tie occurred")
if ties and verbose: if ties and verbose:
print(tiebreaking_message[:-2]) print(tiebreaking_message[:-2])
return representatives return representatives
@ -225,43 +244,50 @@ def __divzero_fewerseatsthanparties(votes, seats, parties, verbose):
# ( see Balinski, M. L., & Young, H. P. (1975). # ( see Balinski, M. L., & Young, H. P. (1975).
# The quota method of apportionment. # The quota method of apportionment.
# The American Mathematical Monthly, 82(7), 701-730.) # The American Mathematical Monthly, 82(7), 701-730.)
def quota(votes, seats, parties=string.ascii_letters, verbose=True): def quota(votes, seats, parties=string.ascii_letters,
tiesallowed=True, verbose=True):
if verbose: if verbose:
print("\nQuota method") print("\nQuota method")
representatives = [0] * len(votes) representatives = [0] * len(votes)
tied = [] while sum(representatives) < seats:
for k in range(1, seats+1):
quotas = [Fraction(votes[i], representatives[i]+1) quotas = [Fraction(votes[i], representatives[i]+1)
for i in range(len(votes))] for i in range(len(votes))]
# check if upper quota is violated # check if upper quota is violated
for i in range(len(votes)): for i in range(len(votes)):
upperquota = int(math.ceil(float(votes[i]) * upperquota = int(math.ceil(float(votes[i]) *
k / sum(votes))) (sum(representatives)+1)
/ sum(votes)))
if representatives[i] >= upperquota: if representatives[i] >= upperquota:
quotas[i] = 0 quotas[i] = 0
chosen = [i for i in range(len(votes))
if quotas[i] == max(quotas)] maxquotas = [i for i in range(len(votes))
if verbose: if quotas[i] == max(quotas)]
if len(chosen) > 1:
tied.append(representatives[chosen[0]]) nextrep = maxquotas[0]
else: representatives[nextrep] += 1
tied = []
representatives[chosen[0]] += 1 if len(maxquotas) > 1 and not tiesallowed:
raise TiesException("Tie occurred")
# print tiebreaking information # print tiebreaking information
if verbose and len(tied) > 0: if verbose and len(maxquotas) > 1:
quotas_now = [Fraction(votes[i], representatives[i]+1)
for i in range(len(votes))]
tiebreaking_message = (" tiebreaking in order of: " + tiebreaking_message = (" tiebreaking in order of: " +
str(parties[:len(votes)]) + str(parties[:len(votes)]) +
"\n ties broken in favor of: ") "\n ties broken in favor of: ")
for i in range(len(tied)): ties_favor = [i for i in range(len(votes))
tiebreaking_message += tied[i] + ", " if quotas_now[i] == quotas_now[nextrep]]
for i in ties_favor:
tiebreaking_message += str(parties[i]) + ", "
tiebreaking_message = (tiebreaking_message[:-2] + tiebreaking_message = (tiebreaking_message[:-2] +
"\n to the disadvantage of: ") "\n to the disadvantage of: ")
for i in range(1, len(chosen)): for i in maxquotas[1:]:
tiebreaking_message += tied[i] + ", " tiebreaking_message += str(parties[i]) + ", "
print(tiebreaking_message) print(tiebreaking_message[:-2])
if verbose: if verbose:
__print_results(representatives, parties) __print_results(representatives, parties)
return representatives return representatives

38
apportionment/unittests.py
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@ -5,10 +5,6 @@ import unittest
import apportionment.methods as app import apportionment.methods as app
METHODS = ["quota", "largest_remainder", "dhondt", "saintelague",
"modified_saintelague", "huntington", "adams", "dean"]
class TestApprovalMultiwinner(unittest.TestCase): class TestApprovalMultiwinner(unittest.TestCase):
def test_all_implemented(self): def test_all_implemented(self):
@ -32,7 +28,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
votes = [14, 28, 7, 35] votes = [14, 28, 7, 35]
seats = 12 seats = 12
for method in METHODS: for method in app.METHODS:
result = app.compute(method, votes, result = app.compute(method, votes,
seats, verbose=False) seats, verbose=False)
self.assertEqual(result, [2, 4, 1, 5], self.assertEqual(result, [2, 4, 1, 5],
@ -43,7 +39,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
votes = [0, 14, 28, 0, 0] votes = [0, 14, 28, 0, 0]
seats = 6 seats = 6
for method in METHODS: for method in app.METHODS:
result = app.compute(method, votes, result = app.compute(method, votes,
seats, verbose=False) seats, verbose=False)
self.assertEqual(result, [0, 2, 4, 0, 0], self.assertEqual(result, [0, 2, 4, 0, 0],
@ -54,13 +50,13 @@ class TestApprovalMultiwinner(unittest.TestCase):
votes = [10, 9, 8, 8, 11, 12] votes = [10, 9, 8, 8, 11, 12]
seats = 3 seats = 3
for method in METHODS: for method in app.METHODS:
result = app.compute(method, votes, result = app.compute(method, votes,
seats, verbose=False) seats, verbose=False)
self.assertEqual(result, [1, 0, 0, 0, 1, 1], self.assertEqual(result, [1, 0, 0, 0, 1, 1],
msg=method + " failed") msg=method + " failed")
# example taken from # examples taken from
# Balinski, M. L., & Young, H. P. (1975). # Balinski, M. L., & Young, H. P. (1975).
# The quota method of apportionment. # The quota method of apportionment.
# The American Mathematical Monthly, 82(7), 701-730. # The American Mathematical Monthly, 82(7), 701-730.
@ -111,7 +107,7 @@ class TestApprovalMultiwinner(unittest.TestCase):
votes = [2, 1, 1, 2, 2] votes = [2, 1, 1, 2, 2]
seats = 2 seats = 2
for method in METHODS: for method in app.METHODS:
result = app.compute(method, votes, result = app.compute(method, votes,
seats, verbose=False) seats, verbose=False)
self.assertEqual(result, [1, 0, 0, 1, 0], self.assertEqual(result, [1, 0, 0, 1, 0],
@ -161,8 +157,28 @@ class TestApprovalMultiwinner(unittest.TestCase):
r2 = app.compute("modified_saintelague", votes, r2 = app.compute("modified_saintelague", votes,
seats, verbose=False) # [4, 0] seats, verbose=False) # [4, 0]
self.assertNotEqual(r1, r2, self.assertNotEqual(r1, r2,
"Saintelague and its modified variant" "Sainte Lague and its modified variant"
+ "should produce differents results.") + "should produce different results.")
def test_no_ties_allowed(self):
self.longMessage = True
votes = [11, 11, 11]
seats = 4
for method in app.METHODS:
with self.assertRaises(app.TiesException,
msg=method + " failed"):
app.compute(method, votes, seats,
tiesallowed=False, verbose=False)
def test_no_ties_allowed2(self):
self.longMessage = True
votes = [12, 12, 11, 12]
seats = 3
for method in app.METHODS:
self.assertEqual(
app.compute(method, votes, seats,
tiesallowed=False, verbose=False),
[1, 1, 0, 1], msg=method + " failed")
if __name__ == '__main__': if __name__ == '__main__':