[Python] How to insert NULL AS alias "dummy columns" for UNION in SQLAlchemy?

Context


Suppose I have a model class in SQLAlchemy that looks something like this:

class A():
id = Column('id', Integer, primary_key=True, autoincrement=True)
title = Column('Title', String, nullable=False)
type = Column('type', String)
message = Column('message', String, nullable=False)


If I filter this model class using query() like this: q = session.query(A) The output is the following:

SELECT
"A"."id" AS "A_id", "A"."title" AS "A_title", "A"."type" AS "A_type", "A"."message" AS "A_message"
FROM "A"

Problem


I need to perform a UNION with another query that contains the same number of columns, in the same order. I need my query to be this:

SELECT
NULL AS "A_id", NULL AS "A_title", NULL AS "A_type", NULL AS "A_message"
FROM "A"


I've already tried: q = session.query(A, null()) but that just returns:

SELECT
"A"."id" AS "A_id", "A"."title" AS "A_title", "A"."type" AS "A_type", "A"."message" AS "A_message", NULL AS anon_1
FROM "A"

Question


SELECT
NULL AS "A_id", NULL AS "A_title", NULL AS "A_type", NULL AS "A_message"
FROM "A"


How can I achieve the query shown above (inserting NULL AS as an alias)?

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