Numpy Array of Sets

[Luis José Novoa]

Hi All, 

Hope you're doing great. One quick question. I am defining an array of sets using numpy as:

a=array([set([])]*3)

Now, if I want to add an element to the set in, lets say, a[0], and I use the .add(4) operation, which results in:

array([set([4]), set([4]), set([4])], dtype=object)

which I do not want. If I use the union operator 

a[0] = a[0] | set([4])

then I obtain what I want:

array([set([4]), set([]), set([])], dtype=object)

Can anyone explain whay this happens?

Thank you very much.