python-3.x - Flask 应用程序崩溃(很可能是由于循环导入)

Question

我在这里遵循了本教程: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。教程中到目前为止一切正常:在我项目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)
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我没有发布我的实际应用程序，而是返回并复制了教程中到目前为止他的应用程序，该应用程序可在他的 Mac 上运行。但是抛出与我在 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 代码和命令行使用我的环境。在这里:

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")

模型.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文件是空的

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，第二个文件也需要导入才能读取，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。

最好的解决方案是在 app.py 文件的末尾简单地导入 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 放在 routes.py 的顶部。请记住，在您的应用程序目录中没有 init.py 可能会导致导入困难。

编辑:

正如以前lyanakin 所说，import 语句不必位于文件末尾。相反，它可以在 app 初始化后的任何位置定位:

应用.py:

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