# _Matcher

> **Class** in `langsmith`

📖 [View in docs](https://reference.langchain.com/python/langsmith/_expect/_Matcher)

A class for making assertions on expectation values.

## Signature

```python
_Matcher(
    self,
    client: Optional[ls_client.Client],
    key: str,
    value: Any,
    _executor: Optional[ls_utils.ContextThreadPoolExecutor] = None,
    run_id: Optional[str] = None,
)
```

## Constructors

```python
__init__(
    self,
    client: Optional[ls_client.Client],
    key: str,
    value: Any,
    _executor: Optional[ls_utils.ContextThreadPoolExecutor] = None,
    run_id: Optional[str] = None,
)
```

| Name | Type |
|------|------|
| `client` | `Optional[ls_client.Client]` |
| `key` | `str` |
| `value` | `Any` |
| `_executor` | `Optional[ls_utils.ContextThreadPoolExecutor]` |
| `run_id` | `Optional[str]` |


## Properties

- `key`
- `value`

## Methods

- [`to_be_less_than()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_be_less_than)
- [`to_be_greater_than()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_be_greater_than)
- [`to_be_between()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_be_between)
- [`to_be_approximately()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_be_approximately)
- [`to_equal()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_equal)
- [`to_be_none()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_be_none)
- [`to_contain()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/to_contain)
- [`against()`](https://reference.langchain.com/python/langsmith/_expect/_Matcher/against)

---

[View source on GitHub](https://github.com/langchain-ai/langsmith-sdk/blob/19dc497a3d89638e4cc35db72ea1c29cad35cbbf/python/langsmith/_expect.py#L91)