Update app.py

app.py

@@ -1,5 +1,5 @@
 from llama_index import GPTVectorStoreIndex, SimpleDirectoryReader, LLMPredictor, ServiceContext, StorageContext, load_index_from_storage
-from langchain.chat_models import ChatOpenAI
+from langchain import OpenAI
 import gradio
 import os
 
@@ -9,7 +9,7 @@ def construct_index(directory_path):
     # set number of output tokens
     num_outputs = 256
 
-    _llm_predictor = LLMPredictor(llm=ChatOpenAI(temperature=0.5, model_name="gpt-4", max_tokens=num_outputs))
+    _llm_predictor = LLMPredictor(llm=OpenAI(temperature=0.5, model_name="gpt-4", max_tokens=num_outputs))
 
     service_context = ServiceContext.from_defaults(llm_predictor=_llm_predictor)