Add async support for transform chain (#8205)

libs/langchain/langchain/chains/transform.py

@@ -1,9 +1,16 @@
 """Chain that runs an arbitrary python function."""
-from typing import Callable, Dict, List, Optional
+import functools
+import logging
+from typing import Any, Awaitable, Callable, Dict, List, Optional
 
-from langchain.callbacks.manager import CallbackManagerForChainRun
+from langchain.callbacks.manager import (
+    AsyncCallbackManagerForChainRun,
+    CallbackManagerForChainRun,
+)
 from langchain.chains.base import Chain
 
+logger = logging.getLogger(__name__)
+
 
 class TransformChain(Chain):
     """Chain transform chain output.
@@ -17,8 +24,22 @@ class TransformChain(Chain):
     """
 
     input_variables: List[str]
+    """The keys expected by the transform's input dictionary."""
     output_variables: List[str]
+    """The keys returned by the transform's output dictionary."""
     transform: Callable[[Dict[str, str]], Dict[str, str]]
+    """The transform function."""
+    atransform: Optional[Callable[[Dict[str, Any]], Awaitable[Dict[str, Any]]]] = None
+    """The async coroutine transform function."""
+
+    @staticmethod
+    @functools.lru_cache
+    def _log_once(msg: str) -> None:
+        """Log a message once.
+
+        :meta private:
+        """
+        logger.warning(msg)
 
     @property
     def input_keys(self) -> List[str]:
@@ -42,3 +63,17 @@ class TransformChain(Chain):
         run_manager: Optional[CallbackManagerForChainRun] = None,
     ) -> Dict[str, str]:
         return self.transform(inputs)
+
+    async def _acall(
+        self,
+        inputs: Dict[str, Any],
+        run_manager: Optional[AsyncCallbackManagerForChainRun] = None,
+    ) -> Dict[str, Any]:
+        if self.atransform is not None:
+            return await self.atransform(inputs)
+        else:
+            self._log_once(
+                "TransformChain's atransform is not provided, falling"
+                " back to synchronous transform"
+            )
+            return self.transform(inputs)