Given a list of scores, returns the index of one of those items at random, biased towards the items with the highest scores.

random_index_with_bias.py

"""
Given a list of scores, returns the index of one of those items at random, 
biased towards the items with the highest scores.

e.g. random_index_with_bias([84, 62, 61, 67, 45])

To show it works, run it 1,000,000 times:

>>> scores = {}
>>> for i in range(1000000):
...     r = random_index_with_bias([84, 62, 61, 67, 45])
...     scores[r] = scores.get(r, 0) + 1
>>> scores
{0: 263421, 1: 193768, 2: 191029, 3: 210212, 4: 141570}
"""
import random

def random_index_with_bias(bias_scores):
    rand = random.uniform(0, sum(bias_scores))
    total = 0
    for i, score in enumerate(bias_scores):
        total += score
        if rand <= total:
            return i