文件列表:

.idea (0, 2020-05-26)
.idea\mi4-exercise17.iml (336, 2020-05-26)
ArrayOfFacts.sol (601, 2020-05-26)
smart_contracts.py (2322, 2020-05-26)

# mi4-exercise17 Playing with Smart Contracts using Web3.py Exercises: Playing with Smart Contracts using Web3.py In this exercise, we will use web3.py library for interacting with Ethereum. Its API is derived from the Web3.js JavaScript API and should be familiar to anyone who has used web3.js. The exercise will show how to interact with an already deployed contract on the Ethereum Ropsten Testnet. 1. Set up environment Web3.py requires Python 3. It can be installed using pip as follows. pip install web3 Create a new Python file and import the following: We will need HTTPProvider in order to create our connection to the Ropsten Testnet using Infura.io. Now let’s get the necessary Infura.io provider. Go to https://infura.io/ and click [Get started for free]: Fill out the form and click [Submit]. Then copy the Ropsten URL: In order to get a contract instance of an already deployed contract, we will need its address and application binary interface. For exercise’s purpose, deploy a simple contract storing an array of facts through Remix IDE using MetaMask Ropsten a provider: If you do not have ETHt, use the MetaMask faucet: https://faucet.metamask.io/ Then, copy its address and ABI, and create an instance of the contract. Json library will be needed to the decode the ABI: 2. Writing to the Smart Contract Now that there is an instance of the contract, create a method for writing facts in the smart contract. It will need the instance, a private key/wallet, the address of the private key/wallet and the fact. The library is not recommended to work with Local Private Keys in Production at the moment, so for the exercise we will enable the unaudited features. Because the contract owner can only add facts to this contract, copy his private key and his address. Copy the private key and the address. The address will be needed to easily calculate the nonce: We will create a simple transaction, which adds a fact to the contract, sign it with the private key and send it. In Ropsten Etherscan: Try adding a fact using another private key. 3. Reading from the Smart Contract When reading from a Smart Contract, no wallets or private keys are needed. First, create a method which gets a fact by a given index: Then create a method, which gets how many facts are stored in the contract: What to Submit? Create a zip file (e.g. username-playing-smart-contracts-web3-py.zip) holding the Python file with the methods, a snapshot of the Ropsten Etherscan contract address and its transactions. Submit your zip file as homework at the course Website.

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