迭代价值观

Question

我试图将频率中的所有值相加。所以它将是0 +.1被放入cum_freq，然后是.1 + .2然后等等。我不确定如何在我的for循环中获取频率值。

frequencies = ['a': .1, 'b': .2, 'c': .7]
cum_freq = [0] * 4
cum_freq[0] = 0
for i in range(1, len(cum_freq)):
    cum_freq[i] = cum_freq[i-1] + "how do I get the i-1 value from frequencies?"