Flask 应用程序崩溃（很可能是由于循环导入）

Question

我在这里学习了本教程：https://youtu.be/mISFEwojJmE?t=367。这是一个非常简单的 Flask 应用程序，用于为站点创建用户登录和注册页面。本教程中到目前为止一切正常：在我的项目中的脚本中导入对象时，出现此错误。

错误：

flask.cli.NoAppException
flask.cli.NoAppException: While importing "app", an ImportError was raised:

Traceback (most recent call last):
  File "c:\users\dejar\onedrive\coding\themes & applications\002 static template\install\env\lib\site-packages\flask\cli.py", line 240, in locate_app
    __import__(module_name)
  File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\app.py", line 6, in <module>
    from account import routes
  File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\account\routes.py", line 5, in <module>
    from app import app, now
ImportError: cannot import name 'app' from partially initialized module 'app' (most likely due to a circular import) (C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\app.py)

Traceback (most recent call last)
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\app.py", line 6, in <module>
from account import routes
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\account\routes.py", line 5, in <module>
from app import app, now
During handling of the above exception, another exception occurred:
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 338, in __call__
self._flush_bg_loading_exception()
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 326, in _flush_bg_loading_exception
reraise(*exc_info)
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\_compat.py", line 39, in reraise
raise value
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 314, in _load_app
self._load_unlocked()
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 330, in _load_unlocked
self._app = rv = self.loader()
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 388, in load_app
app = locate_app(self, import_name, name)
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\env\Lib\site-packages\flask\cli.py", line 245, in locate_app
raise NoAppException(
flask.cli.NoAppException: While importing "app", an ImportError was raised:

Traceback (most recent call last):
File "c:\users\dejar\onedrive\coding\themes & applications\002 static template\install\env\lib\site-packages\flask\cli.py", line 240, in locate_app
__import__(module_name)
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\app.py", line 6, in <module>
from account import routes
File "C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\account\routes.py", line 5, in <module>
from app import app, now
ImportError: cannot import name 'app' from partially initialized module 'app' (most likely due to a circular import) (C:\Users\dejar\OneDrive\Coding\Themes & Applications\002 Static Template\Install\app.py)
The debugger caught an exception in your WSGI application. You can now look at the traceback which led to the error.
To switch between the interactive traceback and the plaintext one, you can click on the "Traceback" headline. From the text traceback you can also create a paste of it. For code execution mouse-over the frame you want to debug and click on the console icon on the right side.

You can execute arbitrary Python code in the stack frames and there are some extra helpers available for introspection:

dump() shows all variables in the frame
dump(obj) dumps all that's known about the object

我没有发布我的实际应用程序，而是返回并在教程中复制了他的应用程序，该应用程序在他的 Mac 上运行。但是会抛出与我在 PC 上运行的实际应用程序相同的错误。我还尝试以管理员身份从 VS Code 和命令行使用我的环境。这里是：

文件结构

C:.Root directory for the project
|   app.py
|   tree.txt
|   
+---env
......more evn files and folders
|           
+---static
|   +---css
|   |       normalize.css
|   |       styles.css
|   |       
|   \---js
|           jquery.js
|           
+---templates
|       base.html
|       dashboard.html
|       home.html
|       
+---user
|   |   models.py
|   |   routes.py
|   |   __init__.py
|   |   
|   \---__pycache__
|           routes.cpython-38.pyc
|           __init__.cpython-38.pyc
|           
\---__pycache__
        app.cpython-38.pyc

app.py

from flask import Flask, render_template

# account routes
from user import routes

# create and configure the app, an instance of Flask
app = Flask(__name__)


@app.route("/")
def home():
    return render_template("home.html")


@app.route("/dashboard/")
def dashboard():
    return render_template("dashboard.html")

models.py

from flask import Flask, jsonify


class User:
    def signup(self):
        user = {"_id": "", "name": "", "email": "", "password": ""}
        return jsonify(user), 200
        # if successful, return status code 200 in json format

routes.py

from flask import Flask, render_template

# import the instance of app from app.py
# from file/module import instance
from app import app

# from folder.file import class
from user.models import User


@app.route("/user/signup", methods=["GET"])
def signup():
    return User().signup()

注意：init.py 文件为空

Answer 1

错误消息cannot import name 'app' from partially initialized module 'app' 的意思是，当 Python 编译一个文件时，它需要编译另一个文件——要导入的模块。但是，第二个文件也需要读取导入，这是原始的第一个文件。所以python不能编译一个而不编译另一个。

对此的最佳解决方案是在 app.py 文件的end 处简单地导入 app.routes，如下所示：

from flask import Flask, render_template #imports at the top

#the rest of your code

from app import routes

这应该可以解决问题。

将from app import app 保留在您的 routes.py 顶部。请记住，您的应用目录中没有 init.py 可能会导致导入困难。

编辑：

正如之前所说，import 语句不必位于文件末尾。相反，它可以定位在 app 初始化后的任意点：

app.py：

# create and configure the app, an instance of Flask
app = Flask(__name__)
    
# account routes
from user import routes