Why does an assignment for double-sliced numpy arrays not work?

Question

why do the following lines not work as I expect?

import numpy as np
a = np.array([0,1,2,1,1])
a[a==1][1:] = 3
print a
>>> [0 1 2 1 1]
# I would expect [         


        

Answer 1

It appears you simply can't do an assignment through a double-slice like that.

This works though:

a[numpy.where(a==1)[0][1:]] = 3