为什么在传递递减值的列表"cum_weights“时，"random.choices”总是返回相同的元素？

import random

weights = [0.1, 0.3, 0.2, 0.4]
cum_weights = []
cumulative_sum = 0
for weight in weights:
    cumulative_sum += weight
    cum_weights.append(cumulative_sum)

# 确保累积权重列表是递增的
assert all(cum_weights[i] <= cum_weights[i+1] for i in range(len(cum_weights)-1))

selected_element = random.choices(range(len(weights)), cum_weights=cum_weights)[0]
print(selected_element)

import random

weights = [0.1, 0.3, 0.2, 0.4]
cum_weights = [sum(weights[:i+1]) for i in range(len(weights))]

# 确保累积权重列表是递增的
assert all(cum_weights[i] <= cum_weights[i+1] for i in range(len(cum_weights)-1))

selected_element = random.choices(range(len(weights)), cum_weights=cum_weights)[0]
print(selected_element)