attributeerror

[Juvenal Claros]

hi people
im develop a project in python, but i have a error i dont know why, somebody maybe say where is my wrong??

-->this is my main where i run :

__author__ = 'Juvenal'

import os, sys
from elixir import *
from Model.TipoAsistencia import TipoAsistencia
from Model.Asistencia import Asistencia
from Model.Ciclo import Ciclo
from Model.Curso import Curso
from Model.Estudiante import Estudiante
from Model.Grado import Grado
from Model.Inscripcion import Inscripcion
from Model.Materia import Materia
from Model.Paralelo import Paralelo
from Model.UnidadEducativa import UnidadEducativa

from Model.Evaluacion.Area import Area
from Model.Evaluacion.Actividad import Actividad
from Model.Evaluacion.Nota import Nota
from Model.Evaluacion.Periodo import Periodo

metadata.bind = "sqlite:///"+os.path.abspath(os.getcwd()+"/DataBase/RegistroPedagogico.sqlite")
metadata.bind.echo = True
metadata.bind.engine


if __name__ == "__main__":
    setup_all()
    create_all()

    TipoAsistencia(id=1, tipo="Presente")
    TipoAsistencia(id=2, tipo="Licencia")
    TipoAsistencia(id=3, tipo="Falta")

    session.commit()
"""
    Ciclo(id=1, nivel = "Primario")
    Ciclo(id=2, nivel = "Secundario")

    Paralelo(id='A', color="Rojo")
    Paralelo(id='B', color="Amarillo")
    Paralelo(id='C', color="Verde")
    Paralelo(id='D', color="Azul")
    Paralelo(id='E', color="Negro")

    Grado(id=1, sigla="1")
    Grado(id=2, sigla="2")
    Grado(id=3, sigla="3")
    Grado(id=4, sigla="4")
    Grado(id=5, sigla="5")
    Grado(id=6, sigla="6")

    Area(id=1, dimension="Ser", valor=20)
    Area(id=2, dimension="Saber", valor=30)
    Area(id=3, dimension="Hacer", valor=30)
    Area(id=4, dimension="Decidir", valor=20)

    Periodo(id=1, bimestre="1 Bimestre")
    Periodo(id=2, bimestre="2 Bimestre")
    Periodo(id=3, bimestre="3 Bimestre")
    Periodo(id=4, bimestre="4 Bimestre")

    Inscripcion(id=1, estado="Nuevo")
    Inscripcion(id=2, estado="Retirado/Abandono")
    Inscripcion(id=3, estado="Traslado Emitido")
    Inscripcion(id=4, estado="Traslado Recibido")
    Inscripcion(id=5, estado="Repitente")

    UnidadEducativa(ruc=1, nombre="Col. Padre Jeronimo Usera", ciclos = [Ciclo(id=1, nivel = "Primario")])
    """

-->and this is my ActiveRecord models:

#!/usr/bin/env python
__author__ = 'JDevelop'

import os
from elixir import *

metadata.bind = "sqlite:///"+os.path.abspath(os.getcwd()+"/../DataBase/RegistroPedagogico.sqlite")
metadata.bind.echo = True

class TipoAsistencia(Entity):

    has_field('id', Integer, primary_key=True)
    has_field('tipo', String(15), required = True)

    #has_many('asistencias', of_kind = 'Asistencia', inverse = 'tipo')

    using_options(tablename = 'TipoAsistencia', shortnames = True)

    pass

#!/usr/bin/env python
__author__ = 'JDevelop'

import os
from datetime import datetime
from elixir import *

metadata.bind = "sqlite:///"+os.path.abspath(os.getcwd()+"/../DataBase/RegistroPedagogico.sqlite")
metadata.bind.echo = True


class Asistencia(Entity):

    has_field('id', Integer, primary_key = True)
    has_field('fecha', Date, default = datetime.now)
    has_field('observacion', String(125), nullable = True)

    belongs_to('tipo', of_kind = 'TipoAsistencia', inverse = 'asistencias', field = 'fkTipo', required = True)
    belongs_to('estudiante', of_kind = 'Estudiante', inverse = 'asistencias', field = 'fkEstudiante', required = True, ondelete = 'casacade')

    using_options(tablename = 'Asistencia', shortnames = True)

-->compile the main and thrown me the next error:

C:\Python27\python.exe "E:/software develop/en python/registroPedagogico/main.py"
Traceback (most recent call last):
  File "E:/software develop/en python/registroPedagogico/main.py", line 27, in <module>
    setup_all()
  File "C:\Python27\lib\site-packages\elixir\__init__.py", line 94, in setup_all
    setup_entities(entities)
  File "C:\Python27\lib\site-packages\elixir\entity.py", line 951, in setup_entities
    method()
  File "C:\Python27\lib\site-packages\elixir\entity.py", line 240, in setup_relkeys
    self.call_builders('create_non_pk_cols')
  File "C:\Python27\lib\site-packages\elixir\entity.py", line 481, in call_builders
    getattr(builder, what)()
  File "C:\Python27\lib\site-packages\elixir\relationships.py", line 451, in create_non_pk_cols
    self.create_keys(False)
  File "C:\Python27\lib\site-packages\elixir\relationships.py", line 689, in create_keys
    col = self.field[key_num].column
AttributeError: 'str' object has no attribute 'column'

Process finished with exit code 1

thanks for you answer