Web3.py Tutorial Python

Detailed code tutorial for beginners on using Web3.py, a Python library for interacting with the Ethereum blockchain. In this tutorial, we'll cover the basics of setting up a Web3.py project, connecting to the Ethereum network, and performing common tasks such as reading contract data and sending transactions.

Step 1: Installation

First, let's install Web3.py using pip, the Python package manager. Open your terminal or command prompt and run the following command:

pip install web3

Step 2: Importing the Library

Once Web3.py is installed, you can import it into your Python script or interactive console. Open a new Python file and add the following line at the beginning:

from web3 import Web3

Step 3: Connecting to the Ethereum Network

To interact with the Ethereum network, you need a connection provider. There are several options available, including running a local Ethereum node or using a remote node provider like Infura. In this tutorial, we'll use Infura as our connection provider.

Sign up for an account at https://infura.io/ and create a new project. Once you have your project ID, you can connect to the Ethereum network using the following code:

w3 = Web3(Web3.HTTPProvider('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID'))

Replace YOUR_INFURA_PROJECT_ID with your actual Infura project ID.

Step 4: Checking the Connection

To ensure that the connection to the Ethereum network is successful, you can check the network ID using the w3.net.version property:

network_id = w3.net.version print(f"Connected to network with ID: {network_id}")

Step 5: Working with Ethereum Accounts

To perform transactions on the Ethereum network, you need an Ethereum account. In Web3.py, you can manage accounts using the Account module. To create a new account, use the following code:

account = Account.create() print(f"New account created: {account.address}") print(f"Private key: {account.privateKey.hex()}")

This code will generate a new Ethereum account and display the account address and private key.

Step 6: Loading an Existing Account

If you already have an Ethereum account, you can load it into Web3.py using the private key. For example:

private_key = 'YOUR_PRIVATE_KEY' account=Account.from_key(private_key) print(f"Loaded account: {account.address}")

Replace YOUR_PRIVATE_KEY with your actual private key.

Step 7: Retrieving Account Balance

You can retrieve the balance of an Ethereum account using the w3.eth.getBalance() method. Here's an example:

balance = w3.eth.getBalance(account.address) print(f"Account balance: {w3.fromWei(balance, 'ether')} ETH")

This code will display the account balance in Ether.

Step 8: Interacting with Smart Contracts

Web3.py provides a convenient way to interact with smart contracts on the Ethereum network. To do this, you'll need the contract's address and ABI (Application Binary Interface). The ABI defines the contract's functions, arguments, and return types.

Assuming you have the contract's address and ABI, you can create a contract instance using the following code:

contract_address = 'CONTRACT_ADDRESS' contract_abi=[...] # Your contract ABI contract=w3.eth.contract(address=contract_address, abi=contract_abi)

Replace CONTRACT_ADDRESS with the actual contract address and provide the contract's ABI as a Python list in the contract_abi variable.

Once you have the contract instance, you can interact with its functions. For example, let's assume there is a getBalance() function in the contract that returns the balance of an address. You can call this function using the following code:

 balance=contract.functions.getBalance(account.address).call() print(f"Contract balance: {balance}")

This code will retrieve the balance from the smart contract.

Step 9: Sending Transactions

To send a transaction to a smart contract, you'll need to sign the transaction using the account's private key. Assuming there is a transfer() function in the contract that transfers tokens from one address to another, you can send a transaction with the following code:

to_address = 'RECIPIENT_ADDRESS' amount=100 # Number of tokens to transfer transaction=contract.functions.transfer(to_address, amount).buildTransaction({ 'from': account.address, 'nonce': w3.eth.getTransactionCount(account.address), 'gas': 200000, 'gasPrice': w3.toWei('40', 'gwei') }) signed_txn=w3.eth.account.signTransaction(transaction, account.privateKey) transaction_hash=w3.eth.sendRawTransaction(signed_txn.rawTransaction) print(f"Transaction sent: {transaction_hash.hex()}")

Replace RECIPIENT_ADDRESS with the recipient's Ethereum address. Adjust the gas and gasPrice values according to your needs.

This code will construct and sign a transaction, and then send it to the Ethereum network. The transaction hash will be displayed.

Step 10: Handling Transaction Receipts

After sending a transaction, you can retrieve the transaction receipt to get information about its status and events emitted by the contract. Use the transaction hash to fetch the receipt:

transaction_receipt = w3.eth.getTransactionReceipt(transaction_hash) print(f"Transaction status: {transaction_receipt['status']}") print(f"Gas used: {transaction_receipt['gasUsed']}")

This code will display the transaction status (either 0 or 1) and the amount of gas used.

That's it! You now have a basic understanding of how to use Web3.py to interact with the Ethereum network, manage accounts, read contract data, and send transactions. Remember to handle exceptions and error cases appropriately in your code when working with real-world applications.

What is Web3.py?

Web3.py is a Python library that allows developers to interact with the Ethereum blockchain. It provides a convenient and easy-to-use interface for interacting with smart contracts, managing Ethereum accounts, sending transactions, and querying blockchain data.

How do I install Web3.py?

You can install Web3.py using the Python package manager, pip. Open your terminal or command prompt and run the command: pip install web3.

How do I connect to the Ethereum network using Web3.py?

To connect to the Ethereum network, you need a connection provider such as Infura. You can sign up for an account at https://infura.io/, create a project, and obtain your Infura project ID. Then, use the following code to connect:

from web3 import Web3 w3=Web3(Web3.HTTPProvider('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID'))

Replace YOUR_INFURA_PROJECT_ID with your actual Infura project ID.

How can I check if my connection to the Ethereum network is successful?

You can check the network ID using the w3.net.version property. 

For example:

network_id = w3.net.version print(f"Connected to network with ID: {network_id}")

How do I interact with smart contracts using Web3.py?

To interact with smart contracts, you'll need the contract's address and ABI (Application Binary Interface). You can create a contract instance using the following code:

contract = w3.eth.contract(address=contract_address, abi=contract_abi)

Replace contract_address with the actual contract address and provide the contract's ABI.

How do I send transactions using Web3.py?

To send a transaction to a smart contract, you'll need to sign the transaction with an Ethereum account's private key. Here's an example code snippet:

transaction = contract.functions.transfer(to_address, amount).buildTransaction({ 'from': account_address, 'nonce': w3.eth.getTransactionCount(account_address), 'gas': 200000, 'gasPrice': w3.toWei('40', 'gwei') }) signed_txn=w3.eth.account.signTransaction(transaction, private_key) transaction_hash=w3.eth.sendRawTransaction(signed_txn.rawTransaction)

Make sure to replace to_address with the recipient's address, adjust the gas and gas price values accordingly, and provide the account address and private key for signing the transaction.

How can I retrieve transaction receipts using Web3.py?

After sending a transaction, you can retrieve the transaction receipt using the transaction hash. Here's an example:

transaction_receipt = w3.eth.getTransactionReceipt(transaction_hash)

The transaction_receipt object contains information such as the transaction status and the amount of gas used.