避免Python中的循环导入

Question

我知道这个问题已经被回答过了，但是对于我的应用程序来说，我无法解决它。我想做的是使用MongoAlchemy设置数据库，而不是使用MongoClient。我希望为每个操作都有不同的脚本。以下是我的主文件app.py：

import os

from flask import Flask, jsonify
from blueprints.db import insert_db
from blueprints.delete_blueprint import delete_bp
from blueprints.insert_blueprint import insert_bp
from blueprints.read_blueprint import read_bp
from blueprints.login_update_blueprint import log_update
import traceback

app = Flask(__name__)

app.register_blueprint(log_update)
app.register_blueprint(read_bp)
app.register_blueprint(insert_bp)
app.register_blueprint(delete_bp)

# database configuration
app.config['MONGOALCHEMY_DATABASE'] = 'rest_api'

# populate table with initial values
insert_db.populateTables()

# mail configuration
app.config['MAIL_SERVER'] = 'smtp.gmail.com'
app.config['MAIL_PORT'] = 465
app.config['MAIL_USERNAME'] = '[e-mail]'
app.config['MAIL_PASSWORD'] = ''
app.config['MAIL_USE_TLS'] = False
app.config['MAIL_USE_SSL'] = True


@app.errorhandler(404)
def page_not_found(c):
    return 'The required page does not exist'


@app.errorhandler(400)
def bad_req(c):
    return 'Bad request. Please review the request'


@app.errorhandler(Exception)
def handle_Exception(error):
    print("\n ______ ERROR ______\n")
    print(traceback.format_exc())
    print("_____________________\n")

    response = dict()
    response['message'] = "A PROBLEM HAS OCCURED, PLEASE TRY AGAIN LATER"
    response['status_code'] = 500
    response = jsonify(response)
    response.status_code = 500

    return response


if __name__ == '__main__':
    app.secret_key = os.urandom(12)
    app.run(debug=True, threaded=True)

请注意，我正在修改旧版本，因此导入仍然存在。当我尝试从app.py中导入app到初始化数据库的脚本时，会出现循环导入的问题，如下所述：

from flask import current_app
from flask_mongoalchemy import MongoAlchemy
# from app import app

db = MongoAlchemy(current_app)


class People(db.Document):
    Name = db.StringField()
    Age = db.IntField()
    Password = db.StringField()
    Vms = db.AnythingField()

如果我试图使用current_app, 我会得到这个错误信息: RuntimeError: Working outside of application context. 这意味着应用程序当前未初始化。如果我从app.py导入应用程序，就会出现循环依赖的问题。 如果我的表述不够清晰，请随时向我询问更多细节。

- SwiftCaller

Answer 1

我愿意将所有的扩展放在一个名为extensions.py的文件中，并创建一个函数来初始化和配置应用程序实例。

extensions.py

from flask_mongoalchemy import MongoAlchemy

db = MongoAlchemy()

models.py

from extensions import db

class Person(db.Model):
    pass

flaskr.py

from flask import Flask
from extensions import db

def create_app():
    app = Flask(__name__)
    db.init_app(app)

    return app

app = create_app()
app.run()

- DobleL