Update app.py

app.py

@@ -15,6 +15,7 @@ from langchain.vectorstores import Chroma
 from langchain.chains import RetrievalQA
 
 from langchain.memory import ConversationBufferMemory
+from langchain.chains import ConversationChain
 
 def loading_pdf():
     return "Loading..."
@@ -26,7 +27,16 @@ def pdf_changes(pdf_doc):
     db = Chroma.from_documents(texts, embeddings)
     retriever = db.as_retriever()
     global qa 
-    qa = RetrievalQA.from_chain_type(llm=OpenAI(temperature=0.5), chain_type="stuff", memory=ConversationBufferMemory(), retriever=retriever, return_source_documents=True)
+    qa = RetrievalQA.from_chain_type(
+        llm=OpenAI(temperature=0.5), 
+        chain_type="stuff", 
+        conversation = ConversationChain(
+            llm=llm, 
+            verbose=True,
+            memory=ConversationBufferMemory()
+        ), 
+        retriever=retriever, 
+        return_source_documents=True)
     return "Ready"
 
 def add_text(history, text):