AWS Ubuntu部署Flask应用报错：'Flask'对象不可迭代

在AWS Ubuntu服务器部署Flask应用时，Gunicorn日志显示处理/favicon.ico请求时出现如下错误，自行排查未解决：

错误日志 #

[2023-12-29 22:32:39 +0000] [5686] [ERROR] Error handling request /favicon.ico
Traceback (most recent call last):
  File "/home/ubuntu/venv/lib/python3.10/site-packages/gunicorn/workers/sync.py", line 135, in handle
    self.handle_request(listener, req, client, addr)
  File "/home/ubuntu/venv/lib/python3.10/site-packages/gunicorn/workers/sync.py", line 183, in handle_request
    for item in respiter:
TypeError: 'Flask' object is not iterable

相关代码 #

main.py #

from myAPP import create_app
from flask_mail import Mail
import base64  # 补充缺失的导入

app = create_app()

@app.template_filter('custom_b64encode')
def custom_b64encode(data):
    return base64.b64encode(data).decode('utf-8')

from flask import render_template

@app.errorhandler(404)
def not_found_error(error):
    return render_template('404.html'), 404

# 移除重复注册的蓝图，create_app中已完成注册
# from myAPP.views import views
# app.register_blueprint(views, name='my_views')

app.config['UPLOAD_FOLDER'] = '/photos/'

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

init.py #

import os
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask_login import LoginManager
from flask_mail import Mail

db = SQLAlchemy()
DB_NAME = "database.db"
mail = Mail()  # 全局初始化mail
UPLOAD_FOLDER = '/photos/'  # 定义UPLOAD_FOLDER

def create_app():
    # 移除错误添加的environ和start_response参数
    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = f'sqlite:///{DB_NAME}'
    app.config['SECRET_KEY'] = 'SecretKey'
    app.config['SECURITY_PASSWORD_SALT'] = 'SecurityPasswordSalt'
    
    app.config['MAIL_SERVER'] = 'example.home.pl'
    app.config['MAIL_PORT'] = 587
    app.config['MAIL_USE_TLS'] = True
    app.config['MAIL_USE_SSL'] = False
    app.config['MAIL_USERNAME'] = os.environ.get('MAIL_USERNAME', 'username')
    app.config['MAIL_PASSWORD'] = os.environ.get('MAIL_PASSWORD', 'password')
    app.config['MAIL_DEFAULT_SENDER'] = 'defaultSender@example.com'
 
    db.init_app(app)
    mail.init_app(app)  

    with app.app_context():
        db.create_all()

    from .views import views
    from .auth import auth

    app.register_blueprint(views, url_prefix='/')
    app.register_blueprint(auth, url_prefix='/')

    from .models import User, Photo

    login_manager = LoginManager()
    login_manager.login_view = 'auth.loginPage'
    login_manager.init_app(app)

    @login_manager.user_loader
    def load_user(id):
        return User.query.get(int(id))
    
    from . import models

    with app.app_context():
        db.create_all()
    return app

app = create_app()
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

from itsdangerous import URLSafeTimedSerializer
s = URLSafeTimedSerializer(app.config['SECRET_KEY'])

问题原因及修复步骤 #

核心问题 #

create_app函数被错误添加了environ和start_response参数——这是WSGI应用的回调签名，但create_app是Flask应用工厂函数，返回的是Flask实例。Gunicorn会将请求参数传给应用入口，若指向带WSGI参数的工厂函数，会导致把Flask实例当作可迭代的响应对象处理，触发TypeError。

修复步骤 #

1. 修正create_app函数签名：移除create_app的environ=None, start_response=None参数，恢复为无参的应用工厂函数（如上述__init__.py代码所示）。
2. 移除重复蓝图注册：main.py中重复注册了views蓝图，create_app内已完成注册，需删除该部分代码避免路由冲突。
3. 补充缺失的导入：main.py中使用base64但未导入，需添加import base64。
4. 修正UPLOAD_FOLDER未定义问题：在__init__.py开头定义UPLOAD_FOLDER，避免末尾配置时出错。
5. 正确配置Gunicorn启动命令：确保启动时指向已创建的Flask实例，而非工厂函数。例如：

   gunicorn main:app --bind 0.0.0.0:8000
   

   或指向myAPP模块中的app实例：

   gunicorn myAPP:app --bind 0.0.0.0:8000
   

内容的提问来源于stack exchange，提问作者Mortyk Manu