'Coroutine' Object is Not Iterable When Invoking Chain

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Example Code

# chain invoke
bot_response = await chain.invoke({
    'question': sanitized_question,
    'chat_history': ch
}, {'callbacks': [langfuse_handler]})


# invoke from Runnable Class
@abstractmethod
def invoke(self, input: Input, config: Optional[RunnableConfig] = None) -> Output:
    """Transform a single input into an output. Override to implement.

    Args:
        input: The input to the Runnable.
        config: A config to use when invoking the Runnable.
           The config supports standard keys like 'tags', 'metadata' for tracing
           purposes, 'max_concurrency' for controlling how much work to do
           in parallel, and other keys. Please refer to the RunnableConfig
           for more details.

    Returns:
        The output of the Runnable.
    """

Description

Hello,

I'm encountering an issue when attempting to use the invoke method on a Runnable object. Specifically, I receive an error indicating that a 'coroutine' object is not iterable.
In my code, chain is an instance of a Runnable object. The invoke method is defined in the Runnable class as follows.
When I attempt to call invoke with await, I encounter the error 'coroutine' object is not iterable. I have also tried using ainvoke but the same issue persists.

Troubleshooting Steps
Tried Without await: This resulted in the same error, as the method is designed to be asynchronous.
Tried ainvoke: This also led to the same error, indicating a potential issue with how invoke or ainvoke are being handled.
Question: Is there a known issue or additional configuration required for using invoke and ainvoke with Runnable objects? How can I resolve the 'coroutine' object is not iterable issue in this context?

Any insights or suggestions would be greatly appreciated!

System Info

langchain==0.2.14
langchain-anthropic==0.1.23
langchain-cohere==0.2.3
langchain-community==0.2.12
langchain-core==0.2.35
langchain-experimental==0.0.64
langchain-google-genai==1.0.10
langchain-ollama==0.1.1
langchain-openai==0.1.19
langchain-text-splitters==0.2.2
langchainhub==0.1.21
langfuse==2.44.1
langgraph==0.1.8
langsmith==0.1.106

[dosubot[bot]]

I found a similar unsolved discussion and an open issue that might be relevant to your problem:

1. NotImplementedError: RunnableGenerator(None) only supports async methods (invoke function) ^[1]
2. ainvoke is not asynchronous ^[2]

The suggested solution in the open issue is that Milvus is not supporting asynchronous calls.

To resolve the 'coroutine' object is not iterable issue when using the invoke and ainvoke methods with Runnable objects in LangChain, ensure you are using the appropriate method for synchronous and asynchronous operations. The invoke method is for synchronous execution, while the ainvoke method is for asynchronous execution.

Synchronous Execution

Use the invoke method for synchronous execution:

from langchain_core.runnables import RunnableLambda

def add_one(x: int) -> int:
    return x + 1

sequence = RunnableLambda(add_one)
result = sequence.invoke(2)  # Synchronous call
print(result)  # Output: 3

Asynchronous Execution

Use the ainvoke method for asynchronous execution:

import asyncio
from langchain_core.runnables import RunnableLambda

async def add_one_async(x: int) -> int:
    return x + 1

sequence = RunnableLambda(add_one_async)
result = await sequence.ainvoke(2)  # Asynchronous call
print(result)  # Output: 3

Ensure that you are not mixing synchronous and asynchronous methods incorrectly. If you attempt to use invoke on a coroutine function, it will raise a TypeError:

def invoke(
        self,
        input: Input,
        config: Optional[RunnableConfig] = None,
        **kwargs: Optional[Any],
    ) -> Output:
        if hasattr(self, "func"):
            return self._call_with_config(
                self._invoke,
                input,
                self._config(config, self.func),
                **kwargs,
            )
        else:
            raise TypeError(
                "Cannot invoke a coroutine function synchronously."
                "Use `ainvoke` instead."
            )

Similarly, ensure that ainvoke is used for coroutine functions to avoid the 'coroutine' object is not iterable issue ^[3].

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