sqlalchemy 查询结果增加一个常量新列

import pandas as pd 
from sqlchemy import literal
.... # 其他引用包

tmp_sql = select(Level1.id.label('level1_id'), 
                 literal(None, Text).label('leve1_name'))
with dbSession() as session:
    result = session.execute(tmp_sql)
    df = pd.DataFrame(result.mappings().all())
    print(df.shape)