KeyError: '' : output_key not found [in _get_input_output return inputs[prompt_input_key], outputs[output_key]] about langchain

[keenborder786]

You are not using the correct input_key that goes along with the memory_key. Please see below:

question_generator_template = PromptTemplate(
        input_variables=[ # your input variables are not correct.
    "chat_history",
    "question", 
],
    template= (  
    """
    Combine the chat history and follow up question into a standalone question.
    Chat History: {chat_history}
    Follow up question: {question}
""")
)

question_generator_chain = LLMChain(
    llm=llm,
    prompt=question_generator_template,
)

# Create retrieval chain
retrieval_chain = ConversationalRetrievalChain(
    combine_docs_chain=document_chain,
    question_generator=question_generator_chain,
    retriever=retriever,
    memory=ConversationBufferMemory(memory_key="chat_history", input_key="question") # should use question as input key
)