Update app.py

app.py

@@ -13,6 +13,7 @@ from langchain.schema import Document
 from langchain.memory import ConversationBufferMemory
 from langchain.callbacks.manager import CallbackManager
 from langchain.callbacks.streaming_stdout import StreamingStdOutCallbackHandler
+from langchain.chains import load_qa_with_sources_from_chain_type
 from langchain.llms.base import LLM
 from typing import List, Dict, Any, Optional
 from pydantic import BaseModel