diff --git a/libs/langchain/langchain/smith/evaluation/string_run_evaluator.py b/libs/langchain/langchain/smith/evaluation/string_run_evaluator.py
index e3cd1ddba7..41fcbe8e3f 100644
--- a/libs/langchain/langchain/smith/evaluation/string_run_evaluator.py
+++ b/libs/langchain/langchain/smith/evaluation/string_run_evaluator.py
@@ -127,11 +127,12 @@ class ChainStringRunMapper(StringRunMapper):
 
     input_key: Optional[str] = None
     """The key from the model Run's inputs to use as the eval input.
-    If not provided, will use the only input key or raise an error if there are multiple.
-    """
+    If not provided, will use the only input key or raise an
+    error if there are multiple."""
     prediction_key: Optional[str] = None
     """The key from the model Run's outputs to use as the eval prediction.
-    If not provided, will use the only output key or raise an error if there are multiple."""
+    If not provided, will use the only output key or raise an error
+    if there are multiple."""
 
     def _get_key(self, source: Dict, key: Optional[str], which: str) -> str:
         if key is not None: