Pure functional implementation of D'Hondt method

dhondt.py

# Pure functional implementation of D'Hondt method

from itertools import islice, count
from collections import Counter
from heapq import merge

def percentage(numerator, denominator):
    return 100.0 * numerator / denominator
    
def take(n, it):
    return islice(it, n)
    
def get_party_fractions(votes, name):
    party_fractions = (float(votes) / n for n in count(1))
    return ((-fraction, name) for fraction in party_fractions)

def get_fractions(results):
    sorted_results = sorted(((votes, name) for (name, votes) in results.items()), reverse=True)
    return (get_party_fractions(votes, name) for (votes, name) in sorted_results)

def get_results_over_threshold(results, min_percentage):
    total_votes = sum(results.values())
    return dict((name, votes) for (name, votes) in results.items()
        if percentage(votes, total_votes) >= min_percentage)
    
def dhondt(results, total_seats, min_percentage=0):
    """
    Return the seats distribution of results votes following the D'Hondt method.
        
    >>> dhondt({"A": 10, "B": 8, "C": 3, "D": 2}, 8)
    Counter({'A': 4, 'B': 3, 'C': 1})

    >>> dhondt({"A": 6, "B": 3, "C": 2}, 8, min_percentage=20)
    Counter({'A': 6, 'B': 2})
    """
    results_over_threshold = get_results_over_threshold(results, min_percentage)
    fractions = get_fractions(results_over_threshold)
    assigned_party_names = (name for (fraction, name) in merge(*fractions))
    return Counter(take(total_seats, assigned_party_names))

if __name__ == "__main__":
    import doctest
    doctest.testmod()