Support runnable factories in .configurable_alts() (#12065)

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

@@ -1013,7 +1013,7 @@ class RunnableSerializable(Serializable, Runnable[Input, Output]):
         self,
         which: ConfigurableField,
         default_key: str = "default",
-        **kwargs: Runnable[Input, Output],
+        **kwargs: Union[Runnable[Input, Output], Callable[[], Runnable[Input, Output]]],
     ) -> RunnableSerializable[Input, Output]:
         from langchain.schema.runnable.configurable import (
             RunnableConfigurableAlternatives,

libs/langchain/langchain/schema/runnable/configurable.py

@@ -6,6 +6,7 @@ from abc import abstractmethod
 from typing import (
     Any,
     AsyncIterator,
+    Callable,
     Dict,
     Iterator,
     List,
@@ -287,7 +288,10 @@ class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
 
     which: ConfigurableField
 
-    alternatives: Dict[str, RunnableSerializable[Input, Output]]
+    alternatives: Dict[
+        str,
+        Union[Runnable[Input, Output], Callable[[], Runnable[Input, Output]]],
+    ]
 
     default_key: str = "default"
 
@@ -314,7 +318,12 @@ class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
                 default=self.default_key,
             ),
             *self.default.config_specs,
-        ] + [s for alt in self.alternatives.values() for s in alt.config_specs]
+        ] + [
+            s
+            for alt in self.alternatives.values()
+            if isinstance(alt, RunnableSerializable)
+            for s in alt.config_specs
+        ]
 
     def configurable_fields(
         self, **kwargs: AnyConfigurableField
@@ -333,7 +342,11 @@ class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
         if which == self.default_key:
             return self.default
         elif which in self.alternatives:
-            return self.alternatives[which]
+            alt = self.alternatives[which]
+            if isinstance(alt, Runnable):
+                return alt
+            else:
+                return alt()
         else:
             raise ValueError(f"Unknown alternative: {which}")
 

libs/langchain/tests/unit_tests/schema/runnable/test_runnable.py

@@ -1,4 +1,5 @@
 import sys
+from functools import partial
 from operator import itemgetter
 from typing import (
     Any,
@@ -925,6 +926,17 @@ def test_configurable_fields() -> None:
     ).invoke({"name": "John"}) == {"llm1": "c", "llm2": "c", "llm3": "d"}
 
 
+def test_configurable_alts_factory() -> None:
+    fake_llm = FakeListLLM(responses=["a"]).configurable_alternatives(
+        ConfigurableField(id="llm", name="LLM"),
+        chat=partial(FakeListLLM, responses=["b"]),
+    )
+
+    assert fake_llm.invoke("...") == "a"
+
+    assert fake_llm.with_config(configurable={"llm": "chat"}).invoke("...") == "b"
+
+
 def test_configurable_fields_example() -> None:
     fake_chat = FakeListChatModel(responses=["b"]).configurable_fields(
         responses=ConfigurableFieldMultiOption(