# ValueError: Unsupported chat history format

**URL:** </static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fvalueerror-unsupported-chat-history-format%2F41622%3E%5C
**Category:** 🔒 Gradio\
**Created:** [May 31, 2023, 12:50pm UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fvalueerror-unsupported-chat-history-format%2F41622 "2023-05-31T12:50:04Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![krpg](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@krpg](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2Fkrpg)%5C
**Post date:** [May 31, 2023, 12:50pm UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fvalueerror-unsupported-chat-history-format%2F41622%2F1 "2023-05-31T12:50:05Z")

</div>

I’m having this issue and cannot see why it’s happening. I have a fairly straightforward setup. It works fine on the first pass-through, when the history is empty. As soon as I try to submit my second prompt, it fails on the line that calls the ConversationalRetrievalChain (`qa({"question": prompt, "chat_history": history})`, and gives me the following error:

`ValueError: Unsupported chat history format: <class 'list'>. Full chat history: [[.....]]`

Here’s my code:

```auto
with gr.Blocks() as demo:
   chatbot = gr.Chatbot()
   msg = gr.Textbox()
   clear = gr.Button("Clear")

   def user(prompt, history):
       response = qa({"question": prompt, "chat_history": history})
       history.append((prompt, response["answer"]))
       return "", history
   
   msg.submit(user, [msg, chatbot], [msg, chatbot], queue=False)
   clear.click(lambda: None, None, chatbot, queue=False)

```

Any idea what could be happening? Thanks in advance.

---

<div class="post-metadata">

**Author:** ![krpg](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@krpg](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2Fkrpg)%5C
**Post date:** [May 31, 2023, 1:38pm UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fvalueerror-unsupported-chat-history-format%2F41622%2F2 "2023-05-31T13:38:51Z")

</div>

I think the issue might be that the return type is a list of list, and the RetrievalChain is expecting a list of tuples

---

<div class="post-metadata">

**Author:** ![Connoropolous](https://avatars.discourse-cdn.com/v4/letter/c/f0a364/32.png) [@Connoropolous](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Fu%2FConnoropolous)%5C
**Post date:** [June 25, 2023, 1:00am UTC](/static-proxy?url=https%3A%2F%2Fdiscuss.huggingface.co%2Ft%2Fvalueerror-unsupported-chat-history-format%2F41622%2F3 "2023-06-25T01:00:43Z")

</div>

For anyone else who ends up here, I was able to eventually debug this when I also ran into it, and to adjust it like this:

```python
        # Convert Gradio's chat history format to LangChain's expected format
        langchain_history = [(msg[1], history[i+1][1] if i+1 < len(history) else "") for i, msg in enumerate(history) if i % 2 == 0]
        # Get response from QA chain
        response = qa({"question": user_message, "chat_history": langchain_history})

```

This code transforms the history into pairs of user messages and responses and passes that into `qa`. Note that the `if i+1 < len(history)` check is necessary to avoid an `IndexError` for the last user message, which doesn’t yet have a corresponding response. For that case, it just uses an empty string as a placeholder.