Understand how SQLAlchemy insert().from_select(..) works

sqlalchemy_insert_from_select.py

import sqlalchemy as sa
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()


class Model(Base):
    __tablename__ = "model"
    id = sa.Column("id", primary_key=True)
    bbb = sa.Column("bbb")
    ccc = sa.Column("ccc")


t = sa.table("ttt", sa.Column("aaa"), sa.Column("bbb"))
query = sa.select(
    [
        Model,
        (Model.ccc.is_(None) | Model.ccc == "").label("ddd_is_empty"),
        Model.bbb.is_(True).label("bbb_is_true"),
    ]
)
print(query)
print(query.columns)

# The first parameter of `from_select(...)` can only be a list of column names.
# If you want to select complex expressions, you must define their aliases
# in the SELECT query.
print(t.insert().from_select(["bbb"], query))


# Output -=======
# SELECT model.id, model.bbb, model.ccc, (model.ccc IS NULL OR model.ccc) = :param_1 AS ddd_is_empty, model.bbb IS true AS bbb_is_true 
# FROM model
# ['id', 'bbb', 'ccc', 'ddd_is_empty', 'bbb_is_true']
# INSERT INTO ttt (bbb) SELECT model.id, model.bbb, model.ccc, (model.ccc IS NULL OR model.ccc) = :param_1 AS ddd_is_empty, model.bbb IS true AS bbb_is_true 
# FROM model