为什么SQLAlchemy create_engine与charset = utf8返回python类型而不是类型？

使用Python 2.7和SQLAlchemy 0.7,我使用以下命令连接到MySQL DB：

engine = create_engine('mysql://username:password@host/dbname?charset=utf8',echo=False)

根据SQLAlchemy文档,设置charset = utf8会自动隐含use_unicode = 1,因此所有字符串都应该以unicode形式返回. http://docs.sqlalchemy.org/en/rel_0_7/dialects/mysql.html具体给出了例子

#set client encoding to utf8; all strings come back as unicode
create_engine(‘mysql+mysqldb:///mydb?charset=utf8’)

那么,为什么当我在映射类中查询文本字段时,该字段最终是否为“str”类型？

Base = declarative_base(engine)

class RegionTranslation(Base):
    ''''''
    __tablename__ = 'RegionTranslation'
    __table_args__ = {'autoload':True}
    def __init__(self,region_id,lang_id,name):
        self.region_id = region_id
        self.lang_id = lang_id
        self.name = name

rtrans = session.query(RegionTranslation).filter_by(region_id = 1,lang_id = 6).one()
print (type(rtrans.name))

输出是