Troubleshooting of Streamlit apps

Troubleshooting of Streamlit Apps: LangChain RAG Integration Issues

I've built a Streamlit application that implements a RAG (Retrieval Augmented Generation) system using LangChain, Pinecone for vector storage, and LLMs (GPT/Claude). The app is experiencing a critical error when attempting to generate responses.

I've checked the logs from "Manage App" in Streamlit Cloud and found this error:

KeyError: "Input to ChatPromptTemplate is missing variables {'Source2', 'page', 'Source1'}.  Expected: ['Source1', 'Source2', 'chat''history', 'context', 'input', 'page'] Received: ['input', 'chat''history', 'context']"

The error trace shows it's failing in langchain_core/prompts/base.py during the validation of input variables, suggesting a mismatch between what my chain provides and what the prompt template expects.

The issue appears to be in my document formatting pipeline. My current implementation:

• Retrieves documents from Pinecone
• Uses a format_docs() function that formats documents as strings
• Passes this to a LangChain prompt template from a Hub that expects additional variables

I've identified that my prompt template needs modification. Currently it contains:

Current Prompt (causing errors):

Markdown format answer[1][2]
# Data Sources
1. {Source1}, p.{page}
2. {Source2}, p.{page}

Proposed Modified Prompt:

Markdown format answer[1][2]
# Data Sources ==
1. <Source1>, p.<page>
2. <Source2>, p.<page>

Be cautious when using curly braces {xxx} in LangChain prompts - they're interpreted as variable placeholders. If you include them in your prompt, you must provide corresponding Python variables to pass these values.