# werkzeug.routing.exceptions.BuildError: Could not build url for endpoint 'auth.login'. Did you mean 'login' instead?

- **ID:** `python/flask-url-for-external-endpoint`
- **Domain:** python
- **Category:** runtime_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

在 url_for 中使用了不存在的端点名称，可能因为蓝图前缀错误或函数名拼写错误。

## Version Compatibility

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

## Workarounds

1. **** (90% success)
   ```
   from flask import Blueprint, url_for
auth_bp = Blueprint('auth', __name__)
@auth_bp.route('/login')
def login(): ...
app.register_blueprint(auth_bp)
# 使用 url_for('auth.login')
   ```
2. **** (85% success)
   ```
   print(app.view_functions.keys())
   ```

## Dead Ends

- **** — 如果蓝图端点实际为 'auth.login'，使用 'login' 会继续报错。 (60% fail)
- **** — 如果蓝图未注册或名称错误，仍然无法构建。 (70% fail)