提示错误如下

C:\Documents and Settings\Administrator\PycharmProjects\flaskr>python manage.py runserver
Traceback (most recent call last):
  File "manage.py", line 7, in 
    from app import create_app
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\__init__.py", line 9, in 
    from .views import init_views
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\views.py", line 8, in 
    from .models import User
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\models.py", line 4, in 
    from . import db
ImportError: cannot import name db

代码如下所示

__init__.py

from  flask import Flask
from flask_bootstrap import Bootstrap
from flask_sqlalchemy import SQLAlchemy
import os
from .views import init_views

basedir = os.path.abspath(os.path.dirname(__file__))

bootstrap = Bootstrap()
db = SQLAlchemy()

#定义create_app函数
def create_app():
    app = Flask(__name__)
#设置密匙
    app.config['SECRET_KEY'] = 'hard to guess string'

#配置数据库
    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////' + os.path.join(basedir,'data.sqlite')
    #app.config['SQLALCHEMY_DATABASE_URL'] = 'sqlite:////' + os.path.join(basedir,'data.sqlite')
    app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
    #app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True

    bootstrap.init_app(app)
    db.init_app(app)
    init_views(app)
    return app

models.py

from . import db

#定义模型
class Role(db.Model):
    __tablename__ = 'roles'
    id = db.Column(db.Integer,primary_key=True)
    name = db.Column(db.String(64),unique=True)
    users = db.relationship('User',backref='role',lazy='dynamic')
    
    def __repr__(self):
        return '' % self.name

class User(db.Model):
    __tablename__ = 'users'
    id = db.Column(db.Integer,primary_key=True)
    username = db.Column(db.String(64),unique=True,index=True)
    role_id = db.Column(db.Integer,db.ForeignKey('roles.id'))

    def __repr__(self):
        return '' %self.username

views.py

from  flask import render_template,make_response,redirect,session,abort
from .forms import NameForm
from .models import User
from . import db

def init_views(app):
    #视图函数
    @app.route('/',methods=['GET','POST'])
    def index(): 
        ##在视图函数中操作数据库
        form = NameForm()
        if form.validate_on_submit():
            user = User.query.filter_by(username=form.name.data).first()
            if user is None:
                user = User(username = form.name.data)
                db.session.add(user)
                session['known']=False
            else:
                session['known']=True
            session['name'] = form.name.data
            form.name.data=''
            return redirect('index')
        return render_template('index.html',form=form,name=session.get('name'),known=session.get('known',False))


    @app.route('/make_response')
    def make_request():
        response = make_response('
Hello!!!
')
        response.set_cookie('answer','42')
        return response

    @app.route('/user/')
    def user(name):
        return render_template('user.html',name=name)

    @app.route('/test/')
    def test_get():
        return render_template('test.html')

    #重定向
    @app.route('/redirect')
    def redirect_test():
        return redirect('http://www.baidu.com')

    @app.route('/abort/')
    def get_abort(id):
        user = load_user(id)
        if not user:
            abort(404)
        return '
Hello,%s
'%user.name

    @app.errorhandler(404)
    def page_not_found(e):
        return render_template('404.html'),404

    @app.errorhandler(500)
    def internal_server_error(e):
        return render_template('500.html'),500

forms.py

from flask_wtf import Form
from wtforms import StringField,SubmitField
from wtforms.validators import Required

##表单类
class NameForm(Form):
    name=StringField('what is you name?',validators=[Required()])
    submit =SubmitField('Submit')