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

- **ID:** `python/flask-session-cookie-error`
- **Domain:** python
- **Category:** config_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Flask requires a secret key to use sessions; without it, session operations fail.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   Set a secure secret key: app.secret_key = os.environ.get('SECRET_KEY', 'dev-key')
   ```
2. **** (90% success)
   ```
   Generate a random key: import secrets\napp.secret_key = secrets.token_hex(16)
   ```

## Dead Ends

- **** — Setting app.secret_key = '' (empty string) is treated as not set. (90% fail)
- **** — Hardcoding a secret key in code is insecure but does work, but doesn't solve deployment issues. (30% fail)