Update app.py

app.py

@@ -9,6 +9,7 @@ from langchain.retrievers import ParentDocumentRetriever
 from langchain.storage import InMemoryStore
 from langchain_chroma import Chroma
 from langchain.llms import LlamaCpp
+from langchain_openai import ChatOpenAI
 from langchain_core.prompts import ChatPromptTemplate, FewShotChatMessagePromptTemplate
 from langchain_core.output_parsers import StrOutputParser
 from langchain_core.runnables import RunnableLambda