如何从 __init__.py 导入应用程序以及为什么会出现此错误？

Question

我想从__init__.py 导入db 到model.py 文件，但我无法导入，出现错误提示：

Traceback (most recent call last):
  File "/home/rohit/Desktop/flask_app/run.py", line 1, in <module>
    from bytewar import create_app
  File "/home/rohit/Desktop/flask_app/bytewar/__init__.py", line 5, in <module>
    from bytewar.user.views import user_blueprint
  File "/home/rohit/Desktop/flask_app/bytewar/user/views.py", line 9, in <module>
    from bytewar.model import Login_form, Login, Post, Contacts, Signup_form, Contacts
  File "/home/rohit/Desktop/flask_app/bytewar/model.py", line 5, in <module>
    from bytewar import db
ImportError: cannot import name 'db'

我的应用程序树：

___ run.py     # <<------- ImportError in this file.
___ bytewar/
  |__ __init__.py
  |__ config.py
  |__ model.py       
  |__ user/
  |   |__ __init__.py
  |   |__ views.py
  |   |__ static/
  |   |    |__ img/
  |   |    |__ ....
  |   |__ template/
  |       |__ index.html
  |       |__ about.html
  |
  |__ admin/
      |__ __init__.py
      |__ views.py
      |__ template/
          |__ index.html
          |__ about.html

__init__.py：

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_bootstrap import Bootstrap 
from flask_login import LoginManager
from bytewar.user.views import user_blueprint
from bytewar.admin.views import admin_blueprint

db = SQLAlchemy()

def create_app():
    app = Flask('bytewar')
    app = Flask(__name__.split('.')[0])
    app.config.from_pyfile('config.py')
    app.config['DEBUG'] = True

    app.register_blueprint(user_blueprint)
    app.register_blueprint(admin_blueprint)

    login_manager = LoginManager()
    bootstrap = Bootstrap(app)

    db.init_app(app)
    login_manager.init_app(app)
    login_manager.session_protection = 'strong'

    return app

在这里你可以看到我已经db.init_app(app)，但我仍然收到ImportError。

在bytewar.user/ 和bytewar.admin/（在views.py 旁边）中添加__init__.py 文件后，run.py 出现错误：

Traceback (most recent call last):
  File "/home/rohit/Desktop/flask_app/run.py", line 1, in <module>
    from bytewar import app
  File "/home/rohit/Desktop/flask_app/bytewar/__init__.py", line 5, in <module>
    from bytewar.user.views import user_blueprint
  File "/home/rohit/Desktop/flask_app/bytewar/user/views.py", line 9, in <module>
    from bytewar.model import Login_form, Login, Post, Contacts, Signup_form, Contacts
  File "/home/rohit/Desktop/flask_app/bytewar/model.py", line 5, in <module>
    from run import db
  File "/home/rohit/Desktop/flask_app/run.py", line 1, in <module>
    from bytewar import app
ImportError: cannot import name 'app'

run.py：

from bytewar import app


if __name__ == "__main__":
    app.run()

我的bytewar/user/__init__.py 和bytewar/admin/__int__.py：

from flask import Blueprint

user_blueprint = Blueprint(
    'user', __name__,
    static_folder='static',
    template_folder='template',
 )

为什么会这样？

Answer 1

在bytewar.user.views 中，您从__init__.py 导入数据库。但是，这仅在导入下方几行定义。因此，在导入完成时，db 尚不存在，错误证实了这一点。当您查看应用程序工厂1 的示例代码时，您会看到app 变量仅在定义后才使用，您的代码也应该这样做。将你的导入移动到底部，然后你就设置好了。

顺便说一句：为什么要在工厂创建app 并立即覆盖它？留下第二个创作。