# ChainStringRunMapper

> **Class** in `langchain_classic`

📖 [View in docs](https://reference.langchain.com/python/langchain-classic/smith/evaluation/string_run_evaluator/ChainStringRunMapper)

Extract items to evaluate from the run object from a chain.

## Signature

```python
ChainStringRunMapper()
```

## Extends

- `StringRunMapper`

## Properties

- `input_key`
- `prediction_key`

## Methods

- [`map()`](https://reference.langchain.com/python/langchain-classic/smith/evaluation/string_run_evaluator/ChainStringRunMapper/map)

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[View source on GitHub](https://github.com/langchain-ai/langchain/blob/8fec4e7ceee2c368b068c49f9fed453276e210e7/libs/langchain/langchain_classic/smith/evaluation/string_run_evaluator.py#L156)