Reading contract state in Blockchain / Solidity - Mini Project: Build & Apply

Reading contract state

📖 Scenario: You are working with a simple blockchain smart contract that stores a greeting message. You want to read the current greeting from the contract.

🎯 Goal: Build a small program that connects to the contract and reads the greeting message stored in its state.

📋 What You'll Learn

Create a variable with the contract address

Create a variable with the contract ABI (Application Binary Interface)

Connect to the blockchain provider

Create a contract instance using the address and ABI

Call the contract's greeting function to read the message

Print the greeting message

💡 Why This Matters

🌍 Real World

Reading contract state is essential for decentralized apps to display current data stored on the blockchain, like balances, messages, or settings.

💼 Career

Blockchain developers often need to read contract state to build user interfaces and verify contract data without changing the blockchain.

1

Set up contract address and ABI

Create a variable called contract_address and set it to the string "0x1234567890abcdef1234567890abcdef12345678". Then create a variable called contract_abi and set it to the list [{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}].

Blockchain / Solidity

# Your code here

Need a hint?

Use a string for the contract address and a list with a dictionary for the ABI.

2

Connect to blockchain provider

Create a variable called provider and set it to a new instance of Web3.HTTPProvider with the URL "https://mainnet.infura.io/v3/YOUR-PROJECT-ID". Then create a variable called w3 and set it to a new Web3 instance using provider.

Blockchain / Solidity

contract_address = "0x1234567890abcdef1234567890abcdef12345678"
contract_abi = [{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}]
# Your code here

Need a hint?

Use Web3.HTTPProvider with the Infura URL and then create a Web3 instance.

3

Create contract instance and read greeting

Create a variable called contract by calling w3.eth.contract with address=contract_address and abi=contract_abi. Then create a variable called greeting by calling the greet function on contract.functions and using .call() to read the value.

Blockchain / Solidity

from web3 import Web3

contract_address = "0x1234567890abcdef1234567890abcdef12345678"
contract_abi = [{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}]

provider = Web3.HTTPProvider("https://mainnet.infura.io/v3/YOUR-PROJECT-ID")
w3 = Web3(provider)
# Your code here

Need a hint?

Use w3.eth.contract with address and abi, then call the greet function.

4

Print the greeting message

Write a print statement to display the value of the variable greeting.

Blockchain / Solidity

from web3 import Web3

contract_address = "0x1234567890abcdef1234567890abcdef12345678"
contract_abi = [{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"}]

provider = Web3.HTTPProvider("https://mainnet.infura.io/v3/YOUR-PROJECT-ID")
w3 = Web3(provider)

contract = w3.eth.contract(address=contract_address, abi=contract_abi)
greeting = contract.functions.greet().call()
# Your code here

Need a hint?

Use print(greeting) to show the message.