重み付け乱択

weightchoice.py

# coding: utf-8
import random
import bisect


# 手本: http://qiita.com/methane/items/045982489cd7cf3720b3
# 変更点: append のメソッドを追加。
class WeightChoice(object):

    def append(self, item, score):
        self.total += score
        self.range.append(self.total)
        self.items.append(item)

    def __init__(self, L=()):
        self.total = 0
        self.range = []
        self.items = []

        for item, score in L:
            self.append(item, score)

    def choice(self):
        if not self.items:
            return None
        r = random.random() * self.total
        idx = bisect.bisect(self.range, r)
        return self.items[idx]