RunnableAssign instantiation raises a pydantic validation error

[B-Step62]

Checked other resources

• I added a very descriptive title to this issue.
• I searched the LangChain documentation with the integrated search.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).

Example Code

The official example from https://api.python.langchain.com/en/latest/runnables/langchain_core.runnables.passthrough.RunnableAssign.html

from typing import Dict
from langchain_core.runnables.passthrough import (
    RunnableAssign,
    RunnableParallel,
)
from langchain_core.runnables.base import RunnableLambda

def add_ten(x: Dict[str, int]) -> Dict[str, int]:
    return {"added": x["input"] + 10}

mapper = RunnableParallel(
    {"add_step": RunnableLambda(add_ten),}
)

runnable_assign = RunnableAssign(mapper)

Error Message and Stack Trace (if applicable)

ValidationError: 1 validation error for RunnableAssign
mapper
  Input should be a valid dictionary or instance of RunnableParallel[dict[str, Any]] [type=model_type, input_value={
  add_step: RunnableLambda(add_ten)
}, input_type=RunnableParallel]
    For further information visit https://errors.pydantic.dev/2.8/v/model_type
File <command-561754153254877>, line 15
      9     return {"added": x["input"] + 10}
     11 mapper = RunnableParallel(
     12     {"add_step": RunnableLambda(add_ten),}
     13 )
---> 15 runnable_assign = RunnableAssign(mapper)
File /local_disk0/.ephemeral_nfs/envs/pythonEnv-412fde62-9d54-4664-ab04-0a1aa6932e45/lib/python3.11/site-packages/langchain_core/runnables/passthrough.py:395, in RunnableAssign.__init__(self, mapper, **kwargs)
    394 def __init__(self, mapper: RunnableParallel[dict[str, Any]], **kwargs: Any) -> None:
--> 395     super().__init__(mapper=mapper, **kwargs)
File /local_disk0/.ephemeral_nfs/envs/pythonEnv-412fde62-9d54-4664-ab04-0a1aa6932e45/lib/python3.11/site-packages/langchain_core/load/serializable.py:110, in Serializable.__init__(self, *args, **kwargs)
    108 def __init__(self, *args: Any, **kwargs: Any) -> None:
    109     """"""
--> 110     super().__init__(*args, **kwargs)
File /databricks/python/lib/python3.11/site-packages/pydantic/main.py:193, in BaseModel.__init__(self, **data)
    191 # `__tracebackhide__` tells pytest and some other tools to omit this function from tracebacks
    192 __tracebackhide__ = True
--> 193 self.__pydantic_validator__.validate_python(data, self_instance=self)

Description

With LangChain 0.3.x, RunnableAssign class cannot be instantiated due to a pydantic validation error. The official example in the class docstring does not work. The mapper argument seems to be correct type (RunnableParallel with dictionary).

System Info

System Information

OS: Linux
OS Version: #74~20.04.1-Ubuntu SMP Tue Aug 6 19:32:13 UTC 2024
Python Version: 3.11.0rc1 (main, Aug 12 2022, 10:02:14) [GCC 11.2.0]

Package Information

langchain_core: 0.3.5
langchain: 0.3.0
langsmith: 0.1.128
langchain_text_splitters: 0.3.0

Optional packages not installed

langgraph
langserve

Other Dependencies

aiohttp: 3.8.5
async-timeout: 4.0.2
httpx: 0.27.0
jsonpatch: 1.33
numpy: 1.24.3
orjson: 3.10.7
packaging: 23.2
pydantic: 2.8.2
PyYAML: 6.0
requests: 2.32.2
SQLAlchemy: 1.4.39
tenacity: 8.2.2
typing-extensions: 4.11.0