gistfile1.py

from sqlalchemy import create_engine, Table, Column, Integer, String, DateTime,MetaData
from sqlalchemy.sql.expression import text
from sqlalchemy.orm import mapper, sessionmaker, validates
from sqlalchemy.orm.util import class_mapper
from sqlalchemy.ext.declarative import declarative_base

class Usuarios(object):
        pass

engine = create_engine("mssql://elusuario:elpassword@www.elsitio.com:1433/pruebas")

Session = sessionmaker( bind = engine )
session = Session()

metadata = MetaData()
metadata.bind = engine
usuarios_table = Table( "usuarios", metadata, autoload = True )
mapper( Usuarios, usuarios_table)

mp =  class_mapper( Usuarios ).columns
for x in mp:
        print x

for row in session.query( Usuarios ).order_by(  Usuarios.Nombre ).all():
        print row.Usuario, row.Nombre, row.Email