检查模型时出现属性错误

我正在django中创建我的第一个模型，我一直在关注与我使用的django版本相比早于django的书，我创建了一个应用程序书并编写了以下模型

from django.db import models

#Create your models here.

    class Publisher(models.Model):
        name = models.CharField(max_length=30)
        address = models.CharField(max_length=50)
        city = models.CharField(max_length=60)
        state_province = models.CharField(max_length=30)
        country = models.CharField(max_length=50)
        website = models.URLField()
    class Author(models.Model):
        first_name = models.CharField(max_length=30)
        last_name = models.CharField(max_length=40)
        email = models.EmailField()
    class Book(models.Model):
        title = models.CharField(max_length=100)
        authors = models.ManyToManyField(Author)
        publisher = models.ForeignKey(Publisher)
        publication_date = models.DateField()

当我使用它检查时，py manage.py检查它给

AttributeError: module 'first' has no attribute 'books'

我的网站结构是 1)first\books(models) 2)first\first 3)first\manage.py

我对设置文件的更改

INSTALLED_APPS = [
    #'django.contrib.admin',
    #'django.contrib.auth',
    #'django.contrib.contenttypes',
    #'django.contrib.sessions',
    #'django.contrib.messages',
    #'django.contrib.staticfiles',
    'first.books' -- I commented the defaults as described in the book
]

MIDDLEWARE_CLASSES = [
    #'django.middleware.security.SecurityMiddleware',
    #'django.contrib.sessions.middleware.SessionMiddleware',
    #'django.middleware.csrf.CsrfViewMiddleware',
    #'django.contrib.auth.middleware.AuthenticationMiddleware',
    #'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    #'django.contrib.messages.middleware.MessageMiddleware',
    #'django.middleware.clickjacking.XFrameOptionsMiddleware'
]

谁能给我一些启示？

我的目录结构

C:\Program Files\Python35\mywebapp\first>tree /f
Folder PATH listing
Volume serial number is CE58-0759
C:.
│   db.sqlite3
│   manage.py
│
├───books
│   │   admin.py
│   │   apps.py
│   │   models.py
│   │   tests.py
│   │   views.py
│   │   __init__.py
│   │
│   └───migrations
│           __init__.py
│
└───first
    │   settings.py
    │   urls.py
    │   views.py
    │   wsgi.py
    │   __init__.py
    │
    ├───template
    │       basic.html
    │
    └───__pycache__
            settings.cpython-35.pyc
            urls.cpython-35.pyc
            views.cpython-35.pyc
            wsgi.cpython-35.pyc
            __init__.cpython-35.pyc

我的settings.py

import os

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))


# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/1.9/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = '*********'

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = True

ALLOWED_HOSTS = []


# Application definition

INSTALLED_APPS = [
    ''''django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles','''
    'first.books',
]

MIDDLEWARE_CLASSES = [
   ''' 'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware','''
]

ROOT_URLCONF = 'first.urls'
import os.path
TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join(os.path.dirname(__file__) ,'template').replace('\\','/')],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'first.wsgi.application'


# Database
# https://docs.djangoproject.com/en/1.9/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}


# Password validation
# https://docs.djangoproject.com/en/1.9/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]


# Internationalization
# https://docs.djangoproject.com/en/1.9/topics/i18n/

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/1.9/howto/static-files/

STATIC_URL = '/static/'