Update app.py

app.py

@@ -72,6 +72,8 @@ READER_MODEL="HuggingFaceH4/zephyr-7b-beta"
 #qa = RetrievalQA.from_chain_type(llm=READER_MODEL,retriever=retriever)
 
 #retrieval_qa_chat_prompt = hub.pull("langchain-ai/retrieval-qa-chat")
+from langchain_core.messages import SystemMessage
+from langchain_core.prompts import HumanMessagePromptTemplate
 
 qa_chat_prompt = ChatPromptTemplate.from_messages(
 [