Troubleshooting of Streamlit apps
Troubleshooting of Streamlit Apps: LangChain RAG Integration Issues[edit]
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[1]:
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> Replace <Source1>, <Source2>, etc., with the actual source names, and <page> with the relevant page numbers if available.
To display curly braces as plain text in your prompt, use double curly braces {{ and }} for escaping. Alternatively, you can replace them with < and > if that fits your use case.
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. 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.[2]