Allow calls to batch() with 0 length arrays (#10627)

This can happen if eg the input to batch is a list generated dynamically, where a 0-length list might be a valid use case

libs/langchain/langchain/llms/base.py

@@ -267,6 +267,9 @@ class BaseLLM(BaseLanguageModel[str], ABC):
         return_exceptions: bool = False,
         **kwargs: Any,
     ) -> List[str]:
+        if not inputs:
+            return []
+
         config = get_config_list(config, len(inputs))
         max_concurrency = config[0].get("max_concurrency")
 
@@ -306,6 +309,9 @@ class BaseLLM(BaseLanguageModel[str], ABC):
         return_exceptions: bool = False,
         **kwargs: Any,
     ) -> List[str]:
+        if not inputs:
+            return []
+
         if type(self)._agenerate == BaseLLM._agenerate:
             # model doesn't implement async batch, so use default implementation
             return await asyncio.get_running_loop().run_in_executor(

libs/langchain/langchain/schema/runnable/base.py

@@ -114,6 +114,9 @@ class Runnable(Generic[Input, Output], ABC):
         Default implementation of batch, which calls invoke N times.
         Subclasses should override this method if they can batch more efficiently.
         """
+        if not inputs:
+            return []
+
         configs = get_config_list(config, len(inputs))
 
         def invoke(input: Input, config: RunnableConfig) -> Union[Output, Exception]:
@@ -144,6 +147,9 @@ class Runnable(Generic[Input, Output], ABC):
         Default implementation of abatch, which calls ainvoke N times.
         Subclasses should override this method if they can batch more efficiently.
         """
+        if not inputs:
+            return []
+
         configs = get_config_list(config, len(inputs))
 
         async def ainvoke(
@@ -376,6 +382,9 @@ class Runnable(Generic[Input, Output], ABC):
     ) -> List[Output]:
         """Helper method to transform an Input value to an Output value,
         with callbacks. Use this method to implement invoke() in subclasses."""
+        if not input:
+            return []
+
         configs = get_config_list(config, len(input))
         callback_managers = [get_callback_manager_for_config(c) for c in configs]
         run_managers = [
@@ -444,6 +453,9 @@ class Runnable(Generic[Input, Output], ABC):
     ) -> List[Output]:
         """Helper method to transform an Input value to an Output value,
         with callbacks. Use this method to implement invoke() in subclasses."""
+        if not input:
+            return []
+
         configs = get_config_list(config, len(input))
         callback_managers = [get_async_callback_manager_for_config(c) for c in configs]
         run_managers: List[AsyncCallbackManagerForChainRun] = await asyncio.gather(
@@ -748,6 +760,9 @@ class RunnableWithFallbacks(Serializable, Runnable[Input, Output]):
         if return_exceptions:
             raise NotImplementedError()
 
+        if not inputs:
+            return []
+
         # setup callbacks
         configs = get_config_list(config, len(inputs))
         callback_managers = [
@@ -813,6 +828,9 @@ class RunnableWithFallbacks(Serializable, Runnable[Input, Output]):
         if return_exceptions:
             raise NotImplementedError()
 
+        if not inputs:
+            return []
+
         # setup callbacks
         configs = get_config_list(config, len(inputs))
         callback_managers = [
@@ -1004,6 +1022,9 @@ class RunnableSequence(Serializable, Runnable[Input, Output]):
     ) -> List[Output]:
         from langchain.callbacks.manager import CallbackManager
 
+        if not inputs:
+            return []
+
         # setup callbacks
         configs = get_config_list(config, len(inputs))
         callback_managers = [
@@ -1122,6 +1143,9 @@ class RunnableSequence(Serializable, Runnable[Input, Output]):
             AsyncCallbackManager,
         )
 
+        if not inputs:
+            return []
+
         # setup callbacks
         configs = get_config_list(config, len(inputs))
         callback_managers = [

libs/langchain/langchain/schema/runnable/config.py

@@ -97,8 +97,8 @@ def get_config_list(
     Helper method to get a list of configs from a single config or a list of
     configs, useful for subclasses overriding batch() or abatch().
     """
-    if length < 1:
+    if length < 0:
-        raise ValueError(f"length must be >= 1, but got {length}")
+        raise ValueError(f"length must be >= 0, but got {length}")
     if isinstance(config, list) and len(config) != length:
         raise ValueError(
             f"config must be a list of the same length as inputs, "

libs/langchain/langchain/schema/runnable/router.py

@@ -129,6 +129,9 @@ class RouterRunnable(
         return_exceptions: bool = False,
         **kwargs: Optional[Any],
     ) -> List[Output]:
+        if not inputs:
+            return []
+
         keys = [input["key"] for input in inputs]
         actual_inputs = [input["input"] for input in inputs]
         if any(key not in self.runnables for key in keys):
@@ -161,6 +164,9 @@ class RouterRunnable(
         return_exceptions: bool = False,
         **kwargs: Optional[Any],
     ) -> List[Output]:
+        if not inputs:
+            return []
+
         keys = [input["key"] for input in inputs]
         actual_inputs = [input["input"] for input in inputs]
         if any(key not in self.runnables for key in keys):