add.at() method

[Truman]

import numpy as np 
x = np.zeros(10)
np.add.at(x, i, 1)
print(x)

output

Output:
[0. 1. 1. 0. 1. 0. 0. 0. 1. 0.]

I just don't get how this at() method works. X becomes array that contains all zeroes. Then happens what?