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python - SQLAlchemy subquery - average of sums

is there any way how to write the following SQL statement in SQLAlchemy ORM:

SELECT AVG(a1) FROM (SELECT sum(irterm.n) AS a1 FROM irterm GROUP BY irterm.item_id);

Thank you

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sums = session.query(func.sum(Irterm.n).label('a1')).group_by(Irterm.item_id).subquery()
average = session.query(func.avg(sums.c.a1)).scalar()

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