在Django 1.8或更高版本中进行填充时出现“Models aren't loaded yet”错误。

我正在使用这段代码来填充我的数据库：

import os
def populate():
    python_cat = add_cat('Python')
    add_page(cat=python_cat, 
    title="Official Python Tutorial",
    url="http://docs.python.org/2/tutorial/")
    add_page(cat=python_cat,
    title="How to Think like a Computer Scientist",
    url="http://www.greenteapress.com/thinkpython/")
    add_page(cat=python_cat,
    title="Learn Python in 10 minutes",
    url="http://www.korokithakis.net/tutorials/python/")
    django_cat = add_cat(name="Django")
    add_page(cat=django_cat,
    title="Official Django Tutorial",
    url="http://djangoproject.com/en/1.5/intro/tutorial01/")
    add_page(cat=django_cat,
    title="Django Rocks",
    url="http://www.djangorocks.com/")
    add_page(cat=django_cat,
    title="How to Tango with Django",
    url="htttp://www.tangowithdjango.com/")
    frame_cat = add_cat(name="Other Frameworks")
    add_page(cat=frame_cat, 
    title="Bottle",
    url="http://bottlepy.org/docs/dev/")
    add_page(cat=frame_cat, 
    title="Flask",
    url="http://flask.pocoo.org")
    # 打印出我们添加给用户的内容
    for c in Category.objects.all():
        for p in Page.objects.filter(category=c):
            print "- {0} - {1}".format(str(c), str(p))
def add_page(cat, title, url, views=0):
    p = Page.objects.get_or_create(category=cat, title=title, url=url, views=views)[0]
    return p
def add_cat(name):
    c = Category.objects.get_or_create(name=name)
    return c
if __name__ == '__main__':
    print "Starting Rango population script..."
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'p.settings')
    from rango.models import Category, Page
    populate()

运行

python c:\python27\p\populate_rango.py

会出现以下错误：

Staring Rango population script...
Traceback (most recent call last):
File "c:\python27\p\populate_rango.py", line 59, in 
populate()
File "c:\python27\p\populate_rango.py", line 4, in populate
python_cat = add_cat('Python')
File "c:\python27\p\populate_rango.py", line 52, in add_cat
c = Category.objects.get_or_create(name=name)
File "C:\Python27\Lib\site-packages\django\db\models\manager.py", li
manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Python27\Lib\site-packages\django\db\models\query.py", line
et_or_create
return self.get(**lookup), False
File "C:\Python27\Lib\site-packages\django\db\models\query.py", line
clone = self.filter(*args, **kwargs)
File "C:\Python27\Lib\site-packages\django\db\models\query.py", line
ilter
return self._filter_or_exclude(False, *args, **kwargs)
File "C:\Python27\Lib\site-packages\django\db\models\query.py", line
filter_or_exclude
clone.query.add_q(Q(*args, **kwargs))
File "C:\Python27\Lib\site-packages\django\db\models\sql\query.py",
in add_q
clause, require_inner = self._add_q(where_part, self.used_aliases)
File "C:\Python27\Lib\site-packages\django\db\models\sql\query.py",
in _add_q
current_negated=current_negated, connector=connector)
File "C:\Python27\Lib\site-packages\django\db\models\sql\query.py",
in build_filter
lookups, parts, reffed_aggregate = self.solve_lookup_type(arg)
File "C:\Python27\Lib\site-packages\django\db\models\sql\query.py",
in solve_lookup_type
_, field, _, lookup_parts = self.names_to_path(lookup_splitted, se
a())
File "C:\Python27\Lib\site-packages\django\db\models\sql\query.py",
in names_to_path
field, model, direct, m2m = opts.get_field_by_name(name)
File "C:\Python27\Lib\site-packages\django\db\models\options.py", li
get_field_by_name
cache = self.init_name_map()
File "C:\Python27\Lib\site-packages\django\db\models\options.py", li
init_name_map
for f, model in self.get_all_related_m2m_objects_with_model():
File "C:\Python27\Lib\site-packages\django\db\models\options.py", li
get_all_related_m2m_objects_with_model
cache = self._fill_related_many_to_many_cache()
File "C:\Python27\Lib\site-packages\django\db\models\options.py", li
_fill_related_many_to_many_cache
for klass in self.apps.get_models():
File "C:\Python27\Lib\site-packages\django\utils\lru_cache.py", line
rapper
result = user_function(*args, **kwds)
File "C:\Python27\Lib\site-packages\django\apps\registry.py", line 1
_models
*self.check_models_ready()
File "C:\Python27\Lib\site-packages\django\apps\registry.py", line 1
ck_models_ready
raise AppRegistryNotReady("Models aren't loaded yet.")
django.core.exceptions.AppRegistryNotReady: Models aren't loaded yet.*

我的其他文件都没问题，但是出现了这个错误。我正在按照Tango with Django的教程进行，但是该书提到的是Django 1.5.4，而我使用的是Django 1.8，有人能帮我解决吗？