Update app.py

app.py

@@ -27,7 +27,8 @@ from collections import defaultdict, OrderedDict
 from langchain_community.vectorstores import FAISS
 from langchain_community.embeddings import HuggingFaceEmbeddings
 from sentence_transformers import SentenceTransformer
-from langchain.retrievers import BM25Retriever
+# from langchain.retrievers import BM25Retriever
+from langchain_community.retrievers import BM25Retriever
 from langchain.schema import Document
 from langchain_core.tools import tool