# RuntimeError: The session is unavailable because no secret key was set

- **ID:** `python/flask-session-secret-key-missing`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Flask 应用未设置 secret_key，导致会话功能无法使用

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.9 | active | — | — |
| 3.10 | active | — | — |

## Workarounds

1. **在应用中设置 secret_key** (95% success)
   ```
   app.secret_key = 'your-secret-key-here'
   ```
2. **使用环境变量设置密钥** (90% success)
   ```
   import os
app.secret_key = os.environ.get('SECRET_KEY', 'fallback-key')
   ```

## Dead Ends

- **设置 secret_key 为 None** — None 不是有效密钥，仍会引发错误 (90% fail)
- **使用空字符串作为密钥** — 空字符串不安全，且可能被 Flask 拒绝 (70% fail)