Return name of column after comparing cummulative sum with random drawn number

I have a DataFrame in which the sum of the columns is 1, like so:

Out[]: 
cod_mun  ws_1    1_3      4      5_7       8      9_10    11     12    13     14     15     nd
1100015 0.1379  0.273   0.2199  0.1816  0.0566  0.0447  0.0617  0.0015  0   0.0021  0.0074  0.0137
1100023 0.1132  0.2009  0.185   0.2161  0.1036  0.0521  0.0885  0.0044  0.0038  0.0061  0.0181  0.0082

I want to draw a random number

import random
prob = random.random()

And then I want to compare such number with the cummulative sum of the columns from left to right and then return the columns' heading.

For example, if prob = 0.24 the threshold would reach 0.27 in the second column, 0.1379 + 0.273 > 0.24Then I would need to return the name of the column.

It it possible to do that WITHOUT a using 15 elifs?

Such that:

if prob < df.iloc[0]['ws_1']:
    return 'ws_1'
elif prob < df.iloc[0]['ws_1'] + df.iloc[0]['1_3']
    return '1_3'
elif ...