# web3.py — Python Library for Ethereum Blockchain Interaction

> A Python library for interacting with the Ethereum blockchain, providing APIs for reading chain data, sending transactions, and calling smart contracts from Python applications.

## Install

Save in your project root:

# web3.py — Python Library for Ethereum Blockchain Interaction

## Quick Use
```bash
pip install web3
python -c "
from web3 import Web3
w3 = Web3(Web3.HTTPProvider('https://rpc.ankr.com/eth'))
print(f'Latest block: {w3.eth.block_number}')
print(f'Connected: {w3.is_connected()}')
"
```

## Introduction
web3.py is a Python library for interacting with the Ethereum blockchain. It provides a Pythonic interface to JSON-RPC endpoints for querying blocks, sending transactions, deploying and calling smart contracts, and subscribing to on-chain events. It is the standard Ethereum library for the Python ecosystem, comparable to ethers.js in JavaScript.

## What web3.py Does
- Connects to Ethereum nodes via HTTP, WebSocket, or IPC providers
- Reads blockchain state: blocks, transactions, balances, logs, and contract storage
- Sends raw or signed transactions for ETH transfers and contract interactions
- Compiles and interacts with smart contracts using ABI-based contract objects
- Supports middleware for transaction signing, gas estimation, POA chains, and caching

## Architecture Overview
web3.py wraps Ethereum JSON-RPC calls in a Python API organized into modules: `w3.eth` for chain data, `w3.net` for network info, and `w3.geth` / `w3.parity` for client-specific extensions. A provider layer handles the transport (HTTP, WS, IPC), and a middleware pipeline lets users inject signing, gas estimation, and response processing between the application and the node. Contract objects use ABI definitions to encode/decode function calls and event logs.

## Self-Hosting & Configuration
- Install: `pip install web3` (or `pip install web3[tester]` for local testing with eth-tester)
- Connect to a node: `w3 = Web3(Web3.HTTPProvider("https://your-rpc-url"))`
- For local development, use Ganache or Anvil as a local Ethereum node
- Configure middleware: `w3.middleware_onion.inject(middleware, layer=0)` for custom processing
- Set default account and gas parameters: `w3.eth.default_account`, `w3.eth.gas_price`

## Key Features
- Full JSON-RPC coverage for Ethereum execution and consensus layer APIs
- Contract abstraction with ABI-based method calling, event filtering, and log decoding
- Middleware architecture for pluggable transaction signing, gas strategies, and POA support
- ENS (Ethereum Name Service) resolution built in for human-readable addresses
- Async API support via `AsyncWeb3` and `AsyncHTTPProvider` for non-blocking applications

## Comparison with Similar Tools
- **ethers.js** — JavaScript equivalent with similar API surface; web3.py is the Python counterpart
- **web3.js** — the original JavaScript Ethereum library; web3.py offers a more Pythonic interface
- **Brownie** — Python smart contract framework that uses web3.py internally; web3.py is the lower-level library
- **ape** — modern Python framework for smart contracts with plugin architecture; web3.py focuses on node interaction without framework opinions
- **alloy** — Rust Ethereum library; web3.py serves the Python ecosystem where Rust is not practical

## FAQ
**Q: Do I need to run my own Ethereum node?**
A: No. You can use public RPC endpoints (Infura, Alchemy, Ankr) or local development nodes like Anvil or Ganache.

**Q: Can web3.py interact with Layer 2 chains like Arbitrum or Optimism?**
A: Yes. Point the provider to the L2's RPC endpoint. Most EVM-compatible chains work with web3.py out of the box.

**Q: How do I sign transactions without exposing private keys?**
A: Use `w3.eth.account.sign_transaction()` locally, then send the signed raw transaction. Never pass private keys to remote nodes.

**Q: Does web3.py support smart contract events and logs?**
A: Yes. Use `contract.events.EventName.create_filter()` or `w3.eth.get_logs()` to query historical and real-time events.

## Sources
- https://github.com/ethereum/web3.py
- https://web3py.readthedocs.io/

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Source: https://tokrepo.com/en/workflows/asset-e31a3f1a
Author: AI Open Source