How do I extend django zinnia weblog entry

I followed the instruction found here

http://django-blog-zinnia.readthedocs.org/en/latest/how-to/extending_entry_model.html

Unfortunately I am having trouble extending. First strange thing is that - I have to change the way the entry modules are imported:

from

from zinnia.models.entry import Entry
from zinnia.admin.entry import EntryAdmin

to

from zinnia.models import Entry
from zinnia.admin import EntryAdmin

After changing, I then ran the server and went to the admin page but then I got this error.

'RatingAdmin.fieldsets[0][1]['fields']' refers to field 'rating' that is missing from the form.

This is my code admin.py

from django.contrib import admin
from django.utils.translation import ugettext_lazy as _


from zinnia.models import Entry
from zinnia.admin import EntryAdmin

class RatingAdmin(EntryAdmin):
# into the 'Content' fieldset
fieldsets = ((_('Content'), {'fields': (
'title', 'content', 'image', 'status', 'rating')}),) + \
EntryAdmin.fieldsets[1:]

# Unregister the default EntryAdmin
# then register the EntryGalleryAdmin class
admin.site.unregister(Entry)
admin.site.register(Entry, RatingAdmin)

Here is my Abstract class model happy_models.py

from django.db import models
from zinnia.models.entry import EntryAbstractClass

class Happy(models.Model):
    rating = models.CharField(max_length=200)

    def __unicode__(self):
        return u'Rating %s' % self.title

    class Meta(EntryAbstractClass.Meta):
        abstract = True

Here is my zinnia entry base model path in settings.py

ZINNIA_ENTRY_BASE_MODEL = 'happy.happy_models.Happy'

I just noticed this at my console

/zinnia/models.py:30‌​2: RuntimeWarning: happy.happy_models.Happy cannot be imported

Here is my directory setup

happy/
    admin.py
    happy_models.py
    views.py

What I might be doing wrong when extending entry?

I finally found out -- by running the server on interactive mode I was able to debug. The sample code had to be modified to this:-

from zinnia.models import EntryAbstractClass

instead of

from zinnia.models.entry import EntryAbstractClass