SQLAlchemy SELECT COUNT(T) の結果は scalar() で求める

with engine.begin() as connection:
    sql = 'SELECT COUNT(*) FROM samples'
    rows = connection.execute(text(sql))
    count = list(rows)[0][0]

こんな方法ではなく、scalar() を使う
例）

from sqlalchemy import create_engine, text
from sqlalchemy.orm import Session

# 接続情報、username, password, host, port, dbname は設定済
engine = create_engine(f'postgresql://{username}:{password}@{host}:{port}/{dbname}')

def countquery() -> int:
    with Session(autocommit=False, autoflush=True, bind=engine) as session:
        try:
            sql = 'SELECT COUNT(*) FROM samples'
            res = session.execute(text(sql)).scalar()
        except Exception as e:
            print(e)
            raise
        else:
            return res

if __name__ == '__main__':
    c = countquery()
    print('count = %d' % c)

engine.begin()　から実行する場合

with engine.begin() as connection:
   sql = 'SELECT COUNT(*) FROM samples'
   count = connection.execute(text(sql)).scalar()

Session query() で、DB の DUAL表を使う

from sqlalchemy import create_engine, text
from sqlalchemy.orm import Session, registry
import sqlalchemy as db

engine = create_engine(f'postgresql://{username}:{password}@{host}:{port}/{dbname}')

mapper_reg = registry()
Base = mapper_reg.generate_base()

class GenericNumeric(Base):
    __tablename__ = 'dual'
    count = db.Column(db.Numeric, nullable=False, primary_key=True)

def countquery() -> int:
    with Session(autocommit=False, autoflush=True, bind=engine) as session:
        try:
            sql = 'SELECT COUNT(*) FROM samples'
            res = session.query(GenericNumeric).from_statement(text(sql)).scalar()
        except Exception as e:
            print(e)
            raise
        else:
            return res.count 

if __name__ == '__main__':
    c = countquery()
    print('count = %d' % c)

ちょっとナンセンスかな。。。