python-web3-app

Work in progress: Vibe coding a Python web3 app that:

• Connects to the Ethereum Sepolia testnet using web3.py to query the ETH balance of a user-provided address via the CLI.
• Connects to the Solana Devnet using solana-py to query the SOL balance of a user-provided address via the CLI.

This project demonstrates basic Python programming, blockchain interaction, and API development/documentation with FastAPI.

Context

This is a learning exercise where I used AI to help guide me through the process of developing a web3 app that queries the blockchain. As someone actively learning Python, this was extremely helpful and conducive to learning. To that end, I made sure to add comments on every line to document what the code does.

Features

• Connects to the Sepolia testnet via a QuickNode endpoint.
• Prompts users to input an Ethereum address and validates it using web3.py's checksum address conversion.
• Queries and displays the ETH balance of the provided address.
• Includes a FastAPI back-end with endpoints documented.
• Uses Coinbase Wallet for testing with Sepolia test ETH.
• Implements error handling for invalid addresses and connection issues.

Tech stack

• Python 3: The core programming language.
• web3.py (v7.12.0): Python library for Ethereum blockchain interaction.
• python-dotenv: Loads environment variables (e.g., QuickNode API URL) from a .env file.
• FastAPI: Provides a framework for automated API documentaton for all endpoints.
• Coinbase Wallet: Non-custodial wallet for managing Sepolia testnet addresses and test ETH.
• QuickNode: Provides the Sepolia testnet endpoint for blockchain access.
• Render: Hosting platform for deploying the FastAPI backend for public API access.

Prerequisites

• Python 3.6+ installed.
• A Coinbase Wallet set to the Sepolia testnet.
• Test ETH in your Coinbase Wallet’s Sepolia address obtained from a faucet (like PoW Faucet).
  • If you don't have a test wallet loaded with test ETH, any valid Ethereum address will work.
• A QuickNode account with a Sepolia endpoint URL.

Installation

1. Clone the repo:

   git clone https://github.com/nicoalba/python-web3-app.git
   cd python-web3-app

2. Set up a virtual environment:

   python -m venv venv
   source venv/bin/activate  # On Windows: venv\Scripts\activate

3. Install dependencies:

   pip install web3 python-dotenv fastapi uvicorn

4. Configure the environment variables:

   1. Create a .env file in the project root.

   2. Add your QuickNode Sepolia endpoint URL:

      WEB3_PROVIDER_URL=https://your-quicknode-sepolia-url

      You can get your URL by signing up at QuickNode and creating a Sepolia endpoint.

5. Set up Coinbase Wallet:

   1. Install the Coinbase Wallet browser extension.
   2. Switch to the Sepolia testnet in the wallet.
   3. Fund your Sepolia address with test ETH from the QuickNode Ethereum Faucet.

Usage via the CLI

1. Run the script:

   python eth-sol-web3.py

2. Follow the prompt and enter a valid Ethereum or Solana address.

   The script will:

   1. Load the QuickNode or Solana endpoint from the .env file.
   2. Connect to the Sepolia testnet or Solana Devnet and display the latest block number.
   3. Validate the address and display the ETH or SOL balance.

Example output

Looking for .env file at: /path/to/python-web3-app/.env
web3.py version: 7.12.0
WEB3_PROVIDER_URL: https://omniscient-distinguished-sailboat...
Connected to blockchain!
Latest block number: 8693694
Enter an Ethereum address to check balance: 0xYourAddress
ETH balance of 0xYourAddress: 0.1 ETH

Example test addresses

• Ethereum (Sepolia): 0x742d35Cc6634C0532925a3b844Bc454e4438f44e
• Solana (Devnet): 4Nd1mGJqD1bNQcb3KgVsC4MQpRxHBaHCErBp9aZ9bJfF

Usage (API)

1. Run the FastAPI server:

   uvicorn eth-web3-app:app --reload

2. Go to http://localhost:8000/docs in a browser to view interactive API documentation:

   

Live demo

The FastAPI backend is deployed on Render for public access. Go to https://python-web3-app.onrender.com/docs to explore the interactive API documentation and test the endpoints:

• GET /block-number: Get the latest Sepolia testnet block number.
• GET /balance/{address}: Query the ETH balance of a valid Ethereum address.
• GET /solana-balance/{address}: Query the SOL balance of a valid Solana address.

To test the API using curl:

curl https://python-web3-app.onrender.com/block-number
curl https://python-web3-app.onrender.com/balance/0xYourValidAddress

Note: The free-tier Render instance spins down after 15 minutes of inactivity, causing a 30-sec delay on the next request.

Future enhancements

• Add ERC-20 token balance queries for Sepolia test tokens.
• Configure with CORS for cross-origin requests.