RunnableLambda: Add in code docs (#11521)

Add in code docs for Runnable Lambda

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

@@ -1946,8 +1946,41 @@ class RunnableGenerator(Runnable[Input, Output]):
 
 
 class RunnableLambda(Runnable[Input, Output]):
-    """
-    A runnable that runs a callable.
+    """RunnableLambda converts a python callable into a Runnable.
+
+    Wrapping a callable in a RunnableLambda makes the callable usable
+    within either a sync or async context.
+
+    RunnableLambda can be composed as any other Runnable and provides
+    seamless integration with LangChain tracing.
+
+    Examples:
+
+        .. code-block:: python
+
+            # This is a RunnableLambda
+            from langchain.schema.runnable import RunnableLambda
+
+            def add_one(x: int) -> int:
+                return x + 1
+
+            runnable = RunnableLambda(add_one)
+
+            runnable.invoke(1) # returns 2
+            runnable.batch([1, 2, 3]) # returns [2, 3, 4]
+
+            # Async is supported by default by delegating to the sync implementation
+            await runnable.ainvoke(1) # returns 2
+            await runnable.abatch([1, 2, 3]) # returns [2, 3, 4]
+
+
+            # Alternatively, can provide both synd and sync implementations
+            async def add_one_async(x: int) -> int:
+                return x + 1
+
+            runnable = RunnableLambda(add_one, afunc=add_one_async)
+            runnable.invoke(1) # Uses add_one
+            await runnable.ainvoke(1) # Uses add_one_async
     """
 
     def __init__(
@@ -1955,10 +1988,25 @@ class RunnableLambda(Runnable[Input, Output]):
         func: Union[Callable[[Input], Output], Callable[[Input], Awaitable[Output]]],
         afunc: Optional[Callable[[Input], Awaitable[Output]]] = None,
     ) -> None:
+        """Create a RunnableLambda from a callable, and async callable or both.
+
+        Accepts both sync and async variants to allow providing efficient
+        implementations for sync and async execution.
+
+        Args:
+            func: Either sync or async callable
+            afunc: An async callable that takes an input and returns an output.
+        """
         if afunc is not None:
             self.afunc = afunc
 
         if inspect.iscoroutinefunction(func):
+            if afunc is not None:
+                raise TypeError(
+                    "Func was provided as a coroutine function, but afunc was "
+                    "also provided. If providing both, func should be a regular "
+                    "function to avoid ambiguity."
+                )
             self.afunc = func
         elif callable(func):
             self.func = cast(Callable[[Input], Output], func)
@@ -1970,6 +2018,7 @@ class RunnableLambda(Runnable[Input, Output]):
 
     @property
     def InputType(self) -> Any:
+        """The type of the input to this runnable."""
         func = getattr(self, "func", None) or getattr(self, "afunc")
         try:
             params = inspect.signature(func).parameters
@@ -1983,6 +2032,7 @@ class RunnableLambda(Runnable[Input, Output]):
 
     @property
     def input_schema(self) -> Type[BaseModel]:
+        """The pydantic schema for the input to this runnable."""
         func = getattr(self, "func", None) or getattr(self, "afunc")
 
         if isinstance(func, itemgetter):
@@ -2010,6 +2060,7 @@ class RunnableLambda(Runnable[Input, Output]):
 
     @property
     def OutputType(self) -> Any:
+        """The type of the output of this runnable as a type annotation."""
         func = getattr(self, "func", None) or getattr(self, "afunc")
         try:
             sig = inspect.signature(func)
@@ -2033,6 +2084,7 @@ class RunnableLambda(Runnable[Input, Output]):
             return False
 
     def __repr__(self) -> str:
+        """A string representation of this runnable."""
         return f"RunnableLambda({get_lambda_source(self.func) or '...'})"
 
     def _invoke(
@@ -2106,6 +2158,7 @@ class RunnableLambda(Runnable[Input, Output]):
         config: Optional[RunnableConfig] = None,
         **kwargs: Optional[Any],
     ) -> Output:
+        """Invoke this runnable synchronously."""
         if hasattr(self, "func"):
             return self._call_with_config(
                 self._invoke,
@@ -2124,6 +2177,7 @@ class RunnableLambda(Runnable[Input, Output]):
         config: Optional[RunnableConfig] = None,
         **kwargs: Optional[Any],
     ) -> Output:
+        """Invoke this runnable asynchronously."""
         if hasattr(self, "afunc"):
             return await self._acall_with_config(
                 self._ainvoke,