flask的工厂函数无法启用

Question

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 <module>
    from app import create_app
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\__init__.py", line 9, in <module>
    from .views import init_views
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\views.py", line 8, in <module>
    from .models import User
  File "C:\Documents and Settings\Administrator\PycharmProjects\flaskr\app\models.py", line 4, in <module>
    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 '<Role %r>' % 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 '<User %r>' %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('<h1>Hello!!!</h1>')
        response.set_cookie('answer','42')
        return response

    @app.route('/user/<name>')
    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/<id>')
    def get_abort(id):
        user = load_user(id)
        if not user:
            abort(404)
        return '<h1>Hello,%s</h1>'%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')

Answer 1

把__init__.py修改一下就可以了

#!/usr/bin/env python
# coding=utf-8

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()

def create_app():
    app = Flask(__name__)

    app.config['SECRET_KEY'] = 'hard to guess string'

    app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////' + os.path.join(basedir,'data.sqlite')
    app.config['SQLALCHEMY_COMMIT_ON_TEARDOWN'] = True
    app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = True

    bootstrap.init_app(app)
    db.init_app(app)

###下面的就是修改内容###

    from .views import init_views
    init_views(app)

    return app

Answer 2

我也在学flask，可惜工作中用的是PHP。
你import 那句用的有问题。 from . Import db 这句尝试引用自己、也就是python禁止使用的循环引用，当然会报错了。尝试把db的初始化放在另一个文件中、如果在同一个package里面、用from .database import db 是OK的。

另外flask_sqlalchemy这个包是第三方开发的，进行了一些封装，但貌似和最新版flask不太兼容。学习阶段尽量减少第三方库的使用，建议直接读Sqlalchemy的官方文档。

其实还是Django的ORM最好用、可惜Django的坑太多，而且灵活性较低

Answer 3

from . import db 没错的，它会在__init__里找到它。

它无法导入应该是根本没有初始化，我看你没用配置文件直接写在初始化函数create_app()下面，那下面的的init_app()的方法你在哪里导入来的？没有import进来，也看不出继承哪里了。