A brief overview of the dApp library

Hello, Habre!

Today I will tell you about the library dApps for Python — a powerful tool for creating decentralized blockchain-based applications. It offers all the necessary functions for interaction with smart contracts, data management and application security. So, let’s figure out what she can do!

Let’s install the library, since it’s easy:

pip install dapp

Contents

1 The main functions of the dApp library
2 An example of implementation

The main functions of the dApp library

The main task of a dApp is to interact with the blockchain. The library allows you to work with smart contracts, creating and sending transactions.

An example of creating and sending a transaction:

from dapp import Blockchain, Contract

# Инициализация соединения с блокчейном
blockchain = Blockchain('https://your-blockchain-node.com')

# Загрузка контракта
contract = Contract('0xYourContractAddress', blockchain)

# Создание транзакции
tx_data = {
    'from': '0xYourWalletAddress',
    'to': '0xRecipientAddress',
    'value': 1000000000000000000,  # 1 ETH в wei
}

# Отправка транзакции
tx_hash = contract.send_transaction(tx_data)
print(f'Transaction sent: {tx_hash}')

This code initializes the connection to the blockchain, loads the smart contract, and creates a transaction.

Event subscription

Smart contracts can generate events that the application can monitor. For example, here’s how to subscribe to the “Transfer” event:

def handle_transfer(event):
    print(f'Transfer event detected: {event}')

contract.on('Transfer', handle_transfer)

# Бесконечный цикл для ожидания событий
import time
while True:
    time.sleep(1)

Now the application will respond to each Transfer event generated by the smart contract.

Data storage with IPFS

Reliable data storage is an important aspect of decentralized programs. Fortunately, the dApp library integrates with IPFS:

from dapp import IPFS

# Инициализация IPFS
ipfs = IPFS()

# Загрузка файла
file_hash = ipfs.upload('path/to/your/file.txt')
print(f'File uploaded to IPFS with hash: {file_hash}')

# Получение файла
file_content = ipfs.download(file_hash)
print(f'File content: {file_content}')

This is how you can upload files to IPFS and extract them by hash.

Security

Security is a necessity. The dApp implements functions for user authentication using cryptographic methods.

from dapp import Auth

# Инициализация аутентификации
auth = Auth()

# Вход пользователя
user_address = auth.login('username', 'password')
print(f'User logged in: {user_address}')

Users can now log into the app securely.

Working with oracles

Sometimes applications need access to external data. This is where oracles, such as Chainlink, come to the rescue.

An example of requesting data from oracle:

from dapp import Oracle

# Инициализация оракула
oracle = Oracle('0xOracleContractAddress')

# Запрос цены ETH/USD
price = oracle.request_data('ETH/USD')
print(f'Current ETH price: {price}')

This way, you can get up-to-date pricing data and use it in your app.

Multifunctionality

The library also has the ability to work with several blockchains. You can develop applications not only for Ethereum, but also for other platforms.

from dapp import Blockchain

# Инициализация блокчейна Ethereum
eth_blockchain = Blockchain('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID')

# Инициализация Binance Smart Chain
bsc_blockchain = Blockchain('https://bsc-dataseed.binance.org/')

# Пример получения баланса ETH
eth_balance = eth_blockchain.get_balance('0xYourEthereumAddress')
print(f'ETH Balance: {eth_balance}')

# Пример получения баланса BNB
bsc_balance = bsc_blockchain.get_balance('0xYourBinanceAddress')
print(f'BNB Balance: {bsc_balance}')

Utilities for testing

The dApp has built-in features for simulating transactions, checking blockchain status, and creating test accounts. Here’s how you can test a transaction:

from dapp import TestBlockchain

# Инициализация тестового блокчейна
test_blockchain = TestBlockchain()

# Создание тестовой учетной записи
test_account = test_blockchain.create_account()

# Имитация транзакции
test_tx = {
    'from': test_account.address,
    'to': '0xSomeRecipientAddress',
    'value': 500000000000000000,  # 0.5 ETH
}

# Подтверждение транзакции
test_tx_receipt = test_blockchain.send_transaction(test_tx)
print(f'Test Transaction Receipt: {test_tx_receipt}')

Thus, it is possible to test transactions in an isolated environment.

Interaction with DeFi protocols

The dApp library supports integration with DeFi protocols. For example, you can work with Uniswap:

from dapp import Uniswap

# Инициализация Uniswap
uniswap = Uniswap('0xUniswapRouterAddress')

# Обмен токенов
swap_tx = {
    'from': '0xYourWalletAddress',
    'to': '0xTokenToSwapAddress',
    'amount': 1000000000000000000,  # 1 токен в wei
}

# Выполнение обмена
swap_receipt = uniswap.swap_tokens(swap_tx)
print(f'Transaction Receipt: {swap_receipt}')

Management of smart contracts

The dApp can be used to manage the lifecycle of smart contracts: deployment, update, and deletion. An example of contract deployment:

from dapp import ContractManager

# Инициализация менеджера контрактов
contract_manager = ContractManager()

# Развертывание нового контракта
contract_address = contract_manager.deploy('MySmartContract', 'ConstructorArgument')
print(f'Contract deployed at: {contract_address}')

Analytics and monitoring

And finally, the monitoring and analytics functions will help you monitor the state of the application in real time:

from dapp import Analytics

# Инициализация аналитики
analytics = Analytics()

# Получение статистики по транзакциям
tx_stats = analytics.get_transaction_stats('0xYourWalletAddress')
print(f'Transaction Stats: {tx_stats}')

This way you can collect transaction data and use it to optimize your dApp.

An example of implementation

Let’s create a simple decentralized application with a dApp, which will be a simple decentralized market for exchanging tokens. This application will allow users to exchange one token for another, track their balances and interact with smart contracts.

The application will consist of the following components:

Smart contract: The contract that drives the token exchange logic
Frontend: User interface for interacting with the contract
Python code: The server part that uses the dApp library to communicate with the blockchain.

Smart contract:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0 ;

interface IERC20 {
    function transfer(address to, uint256 amount) external returns (bool);
    function balanceOf(address account) external view returns (uint256);
}

contract TokenExchange {
    address public token1;
    address public token2;

    event TokensSwapped(address indexed user, uint256 amountIn, uint256 amountOut);

    constructor(address _token1, address _token2) {
        token1 = _token1;
        token2 = _token2;
    }

    function swap(uint256 amountIn) external {
        require(IERC20(token1).balanceOf(msg.sender) >= amountIn, "Insufficient balance");
        
        uint256 amountOut = amountIn; // Здесь можно добавить логику для расчета количества токенов, возвращаемых в зависимости от курса.
        
        require(IERC20(token1).transferFrom(msg.sender, address(this), amountIn), "Transfer failed");
        require(IERC20(token2).transfer(msg.sender, amountOut), "Transfer failed");

        emit TokensSwapped(msg.sender, amountIn, amountOut);
    }
}

Backend part

Let’s create the server part using the dApp library, which will interact with the smart contract:

from dapp import Blockchain, Contract

# Инициализация соединения с блокчейном
blockchain = Blockchain('https://mainnet.infura.io/v3/YOUR_INFURA_PROJECT_ID')

# Загружаем смарт-контракт
contract_address="0xYourContractAddress"
exchange_contract = Contract(contract_address, blockchain)

def swap_tokens(user_address, amount_in):
    tx_data = {
        'from': user_address,
        'to': contract_address,
        'amount': amount_in,
    }
    tx_hash = exchange_contract.call('swap', tx_data)
    return tx_hash

# Пример использования функции обмена токенов
user_address="0xYourWalletAddress"
amount_to_swap = 1000000000000000000  # 1 токен в wei
transaction_hash = swap_tokens(user_address, amount_to_swap)
print(f'Transaction sent: {transaction_hash}')

Frontend

Let’s create a simple HTML page with JavaScript to interact with our dApp:




    
    
    Token Exchange

How to launch?

Smart contract: We deploy a smart contract on the Ethereum test network using Remix or the same Truffle.
Backend: Make sure your Python code works with the correct smart contract addresses and wallet.
Frontend: Replace 0xYourContractAddress to the address of the smart contract and add the ABI of the contract to JS.

You can read more about the library here.

Finally, I will mention the open lessons that will be held in October as part of the “Development of decentralized applications” course:

October 3: Using RUST to create decentralized applications (Dapps). Record by link
October 23: Using Blockchains to Create Decentralized Applications (DApps). Record by link

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A brief overview of the dApp library