# AsyncIteratorCallbackHandler

> **Class** in `langchain_classic`

📖 [View in docs](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler)

Callback handler that returns an async iterator.

## Signature

```python
AsyncIteratorCallbackHandler(
    self,
)
```

## Extends

- `AsyncCallbackHandler`

## Constructors

```python
__init__(
    self,
) -> None
```


## Properties

- `queue`
- `done`
- `always_verbose`

## Methods

- [`on_llm_start()`](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler/on_llm_start)
- [`on_llm_new_token()`](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler/on_llm_new_token)
- [`on_llm_end()`](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler/on_llm_end)
- [`on_llm_error()`](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler/on_llm_error)
- [`aiter()`](https://reference.langchain.com/python/langchain-classic/callbacks/streaming_aiter/AsyncIteratorCallbackHandler/aiter)

---

[View source on GitHub](https://github.com/langchain-ai/langchain/blob/f0c5a28fa05adcda89aebcb449d897245ab21fa4/libs/langchain/langchain_classic/callbacks/streaming_aiter.py#L14)