python network_error ai_generated true

访问 'http://localhost:5000/api' 被 CORS 策略阻止：请求的资源上没有 'Access-Control-Allow-Origin' 头。

Access to fetch at 'http://localhost:5000/api' from origin 'http://localhost:3000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

ID: python/flask-cors-preflight-failed

其他格式: JSON · Markdown 中文 · English
80%修复率
86%置信度
0证据数
2024-04-19首次发现

版本兼容性

版本状态引入弃用备注
2.x active — — —
3.x active — — —

根因分析

未安装/注册 Flask-CORS，或由于路由限制了方法导致 OPTIONS 预检请求未被处理。

English

Flask-CORS not installed/registered, or OPTIONS preflight not handled because route restricts methods.

generic

解决方案

  1. 95% 成功率 
    from flask_cors import CORS; CORS(app, resources={r'/api/*': {'origins': 'http://localhost:3000'}})
  2. 85% 成功率 
    Ensure route methods include OPTIONS: @app.route('/api', methods=['GET','POST','OPTIONS'])

无效尝试

常见但无效的做法:

  1. 65% 失败

    Preflight OPTIONS still returns 405 before after_request runs.

  2. 90% 失败

    CORS is server-controlled; client cannot bypass it.