weighted_choice.py

from bisect import bisect
from random import random


def weighted_choice(choices):
    if not choices:
        return None

    values, weights = zip(*choices)
    total = 0
    cum_weights = []
    for w in weights:
        total += w
        cum_weights.append(total)
    x = random() * total
    i = bisect(cum_weights, x)
    return values[i]

choices = [(1, 2), (2, 6), (3, 2)]
v1 = 0
v2 = 0
v3 = 0
for i in range(100000):
    v = weighted_choice(choices)
    if v == 1:
        v1 += 1
    if v == 2:
        v2 += 1
    if v == 3:
        v3 += 1
        
print(v1, v2, v3) # (19906, 60172, 19922)