In Sqlalchemy, what's different in defining table using Base and Table

Question

I know i can define a table using Table:

user = Table('user', metadata,
    Column('user_id', Integer, primary_key = True),
)

and using Base:

Base = declarative_base()    
class User(Base):
        __tablename__ = 'user'
        user_id= Column(Integer, primary_key = True)

but what's the different???

Answer 1

Base = declarative_base()

class User(Base):
    __tablename__ = 'user'

    id = Column('id', Integer, primary_key=True)
    name = Column('name', Unicode(64))

is just syntactic sugar for

metadata = MetaData()

user = Table('user', metadata,
    Column('id', Integer, primary_key=True),
    Column('name', Unicode(64)),
)

class User(object):
    pass

mapper(User, user)  # this will modify the User class!