> ## Documentation Index
> Fetch the complete documentation index at: https://docs.galileo.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# validations

## require\_exactly\_one

```python theme={null}
def require_exactly_one(*param_names: str,
```

Decorator to ensure that exactly one of the given keyword arguments is provided (not None).

## Raises

ValidationError: If neither or both parameters are provided.

**Examples**

```python theme={null}
@require_exactly_one("project_id", "project_name")
def list(*, project_id=None, project_name=None):
    ...
```