app.py

import streamlit as st
from langchain_community.document_loaders import PyPDFLoader
from langchain_mistralai.chat_models import ChatMistralAI
from langchain_mistralai.embeddings import MistralAIEmbeddings
from langchain_community.vectorstores import FAISS
from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain.chains.combine_documents import create_stuff_documents_chain
from langchain_core.prompts import ChatPromptTemplate
from langchain.chains import create_retrieval_chain

st.title("PDF Question Answering with LangChain")

# Upload PDF
uploaded_file = st.file_uploader("Upload a PDF file", type=["pdf"])

if uploaded_file:
    with open("uploaded.pdf", "wb") as f:
        f.write(uploaded_file.getbuffer())

    # Load data
    loader = PyPDFLoader("uploaded.pdf")
    docs = loader.load()
    
    # Split text into chunks
    text_splitter = RecursiveCharacterTextSplitter()
    documents = text_splitter.split_documents(docs)
    
    # API Key input
    api_key = st.text_input("Enter your MistralAI API Key", type="password")
    
    if api_key:
        try:
            # Define the embedding model
            embeddings = MistralAIEmbeddings(model="mistral-embed", mistral_api_key=api_key)
            
            # Create the vector store
            vector = FAISS.from_documents(documents, embeddings)
            
            # Define a retriever interface
            retriever = vector.as_retriever()
            
            # Define LLM
            model = ChatMistralAI(mistral_api_key=api_key)
            
            # Define prompt template
            prompt = ChatPromptTemplate.from_template("""Answer the following question based only on the provided context:
            
            <context>
            {context}
            </context>
            
            Question: {input}""")
            
            # Create a retrieval chain to answer questions
            document_chain = create_stuff_documents_chain(model, prompt)
            retrieval_chain = create_retrieval_chain(retriever, document_chain)
            
            # User prompt input
            user_prompt = st.text_input("Enter your question")
            
            if user_prompt:
                with st.spinner("Processing..."):
                    response = retrieval_chain.invoke({"input": user_prompt})
                    if "answer" in response:
                        st.write(response["answer"])
                    else:
                        st.write("No answer found.")
        
        except Exception as e:
            st.error(f"Error: {e}")
            # Print or log detailed error information for debugging
            st.exception(e)

else:
    st.write("Please upload a PDF file to get started.")