Update app.py

added a prompt to the chain

app.py

@@ -3,6 +3,8 @@ import gradio as gr
 from langchain.document_loaders import OnlinePDFLoader
 
 from langchain.text_splitter import CharacterTextSplitter
+from langchain.prompts import PromptTemplate
+
 text_splitter = CharacterTextSplitter(chunk_size=350, chunk_overlap=0)
 
 from langchain.llms import HuggingFaceHub
@@ -22,8 +24,27 @@ def pdf_changes(pdf_doc):
     texts = text_splitter.split_documents(documents)
     db = Chroma.from_documents(texts, embeddings)
     retriever = db.as_retriever()
+    
+    prompt_template = """You have been given a pdf or pdfs. You must search these pdfs. 
+    If you don't know the answer, just say that you don't know, don't try to make up an answer.
+    Only answer the question.
+    
+    {context}
+    
+    Question: {question}
+    Answer:"""
+    PROMPT = PromptTemplate(
+        template=prompt_template, input_variables=["context", "question"]
+    )
+    chain_type_kwargs = {"prompt": PROMPT}
     global qa 
-    qa = RetrievalQA.from_chain_type(llm=flan_ul2, chain_type="stuff", retriever=retriever, return_source_documents=True)
+    qa = RetrievalQA.from_chain_type(
+        llm=flan_ul2, 
+        chain_type="stuff", 
+        retriever=retriever, 
+        return_source_documents=True,
+        chain_type_kwargs=chain_type_kwargs,
+    )
     return "Ready"
 
 def add_text(history, text):