gistfile1.py

    subquery = query.subquery()

    unnest_expr = expr.select(columns=[distinct(func.unnest(subquery.c.attribute_ids))], from_obj=subquery)
    array_expr = expr.select(columns=[func.array(unnest_expr)])


generates:

SELECT array((SELECT DISTINCT unnest(anon_1.attribute_ids) 
FROM (SELECT product.attribute_ids AS attribute_ids 
FROM product) AS anon_1)) AS array_1 
FROM (SELECT DISTINCT unnest(anon_1.attribute_ids) 
FROM (SELECT product.attribute_ids AS attribute_ids 
FROM product) AS anon_1)

I want:

SELECT array((SELECT DISTINCT unnest(anon_1.attribute_ids) 
FROM (SELECT product.attribute_ids AS attribute_ids 
FROM product) AS anon_1)) AS array_1