tengo errores al producir modelForm

[Copia]

Hola, intento seguir el ejemplo de ModalForm de la documentacion oficial de django pero creo que ya lo tengo todo y tengo un error que no se como solucionar,
El error es al mostrar el formulario, y dice:
----------------------------------------
NameError at /new_book/
name 'TITLE_CHOICES' is not defined
Request Method: GET
Request URL: http://127.0.0.1:8000/new_book/
Django Version: 1.3.1
Exception Type: NameError
Exception Value:
name 'TITLE_CHOICES' is not defined


Tengo los codigos como sigue:
cms/mysite/models.py

Código Python:

from django.db import models
from django.forms import ModelForm
 
TITLE_CHOICES = (
    ('MR', 'mr.'),
    ('MRS','Mrs.'),
    ('MS','Ms.'),
)
 
class Author(models.Model):
    name =  models.CharField(max_length=100)
    title = models.CharField(max_length=3, choices=TITLE_CHOICES)
    birth_date = models.DateField(blank=True, null=True)
 
    def __unicode__(self):
        return self.name
 
class Book(models.Model):
    name = models.CharField(max_length=100)
    authors = models.ManyToManyField(Author)
 
class AuthorForm(ModelForm):
    class Meta:
        model = Author
 
class BookForm(ModelForm):
    class Meta:
        model = Book
 

cms/mysite/forms.py

Código Python:

from django import forms
 
class AuthorForm(forms.Form):
    name = forms.CharField(max_length=100)
    title = forms.CharField(max_length=3,
                widget=forms.Select(choices=TITLE_CHOICES))
    birth_date = forms.DateField(required=False)
 
class BookForm(forms.Form):
    name = forms.CharField(max_length=100)
    authors = forms.ModelMultipleChoiceField(queryset=Author.objects.all())
 

cms/mysite/views.py

Código Python:

# Create your views here.
from django.template.loader import get_template
from django.template import Context
from django.http import HttpResponse
from forms import BookForm
 
def new_book(request):
    if request.method == 'POST':
        form = BookForm(request.POST)
        if form.is_valid():
            return HttpResponseRedirect('/new_book/thanks/')
    else :
        form = BookForm()
        return render_to_response('new_book.html',{'form':form,})
 

y las urls los tengo asi:

Código Python:

from cms.mysite import views
 
urlpatterns = patterns('',   
    (r'^new_book/$', views.new_book),
 
)
 

----------------------------
cms/mysite/templates/new_book.html

Código HTML:

<form action="/set_new_book/" method="post">
    <p><label>Name:</label>
       {{ form.name}}
    </p>
    <p><label>Authors:</label>
       {{ form.authors }}
    </p>