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Web3.py Python Library

Intro diagram

Introduction

Web3.py is a set of libraries that allow developers to interact with Ethereum nodes using HTTP, IPC, or WebSocket protocols with Python. Moonbeam has an Ethereum-like API available that is fully compatible with Ethereum-style JSON RPC invocations. Therefore, developers can leverage this compatibility and use the web3.py library to interact with a Moonbeam python3 as if they were doing so on Ethereum.

In this guide, you'll learn how to use the web3.py library to send a transaction and deploy a contract on Moonbase Alpha. This guide can be adapted for Moonbeam, Moonriver, or a Moonbeam development node.

Checking Prerequisites

For the examples in this guide, you will need to have the following:

  • An account with funds. For Moonbase Alpha, you can get DEV tokens for testing purposes from Mission Control
  • To test out the examples in this guide on Moonbeam or Moonriver, you will need to have your own endpoint and API key which you can get from one of the supported Endpoint Providers.

Note

The examples in this guide assumes you have a MacOS or Ubuntu 18.04-based environment and will need to be adapted accordingly for Windows.

Create a Python Project

To get started, you can create a directory to store all of the files you'll be creating throughout this guide:

mkdir web3-examples && cd web3-examples

For this guide, you'll need to install the web3.py library and the Solidity compiler. To install both packages, you can run the following command:

pip3 install web3 py-solc-x

Setup Web3.py with Moonbeam

You can configure web3.py to work with any of the Moonbeam networks. To configure your project for Moonbeam or Moonriver, you will need to have your own endpoint and API key which you can get from one of the supported Endpoint Providers.

The simplest way to get started with each of the networks is as follows:

from web3 import Web3

web3 = Web3(Web3.HTTPProvider('RPC-API-ENDPOINT-HERE')) # Insert your RPC URL here
from web3 import Web3

web3 = Web3(Web3.HTTPProvider('RPC-API-ENDPOINT-HERE')) # Insert your RPC URL here
from web3 import Web3

web3 = Web3(Web3.HTTPProvider('https://rpc.api.moonbase.moonbeam.network'))
from web3 import Web3

web3 = Web3(Web3.HTTPProvider('http://127.0.0.1:9933'))

Send a Transaction

During this section, you'll be creating a couple of scripts. The first one will be to check the balances of your accounts before trying to send a transaction. The second script will actually send the transaction.

You can also use the balance script to check the account balances after the transaction has been sent.

Check Balances Script

You'll only need one file to check the balances of both addresses before and after the transaction is sent. To get started, you can create a balances.py file by running:

touch balances.py

Next, you will create the script for this file and complete the following steps:

  1. Set up the Web3 provider
  2. Define the address_from and address_to variables
  3. Get the balance for the accounts using the web3.eth.get_balance function and format the results using the web3.fromWei
# 1. Add the Web3 provider logic here:
# {...}

# 2. Create address variables
address_from = "ADDRESS-FROM-HERE"
address_to = "ADDRESS-TO-HERE"

# 3. Fetch balance data
balance_from = web3.fromWei(web3.eth.get_balance(address_from), "ether")
balance_to = web3.fromWei(web3.eth.get_balance(address_to), "ether")

print(f"The balance of { address_from } is: { balance_from } ETH")
print(f"The balance of { address_to } is: { balance_to } ETH")

You can view the complete script on GitHub.

To run the script and fetch the account balances, you can run the following command:

python3 balances.py

If successful, the balances for the origin and receiving address will be displayed in your terminal in ETH.

Send Transaction Script

You'll only need one file for executing a transaction between accounts. For this example, you'll be transferring 1 DEV token from an origin address (from which you hold the private key) to another address. To get started, you can create a transaction.py file by running:

touch transaction.py

Next, you will create the script for this file and complete the following steps:

  1. Import the rpc_gas_price_strategy which will be used in the following steps to get the gas price used for the transaction
  2. Set up the Web3 provider
  3. Define the account_from, including the private_key, and the address_to variables. The private key is required to sign the transaction. Note: This is for example purposes only. Never store your private keys in a JavaScript file
  4. Use the Web3.py Gas Price API to set a gas price strategy. For this example, you'll use the imported rpc_gas_price_strategy
  5. Create and sign the transaction using the web3.eth.account.sign_transaction function. Pass in the nonce gas, gasPrice, to, and value for the transaction along with the sender's private_key. To get the nonce you can use the web3.eth.get_transaction_count function and pass in the sender's address. To predetermine the gasPrice you'll use the web3.eth.generate_gas_price function. For the value, you can format the amount to send from an easily readable format to Wei using the web3.toWei function
  6. Using the signed transaction, you can then send it using the web3.eth.send_raw_transaction function and wait for the transaction receipt by using the web3.eth.wait_for_transaction_receipt function
# 1. Import the gas strategy
from web3.gas_strategies.rpc import rpc_gas_price_strategy

# 2. Add the Web3 provider logic here:
# {...}

# 3. Create address variables
account_from = {
    "private_key": "YOUR-PRIVATE-KEY-HERE",
    "address": "PUBLIC-ADDRESS-OF-PK-HERE",
}
address_to = "ADDRESS-TO-HERE"

print(
    f'Attempting to send transaction from { account_from["address"] } to { address_to }'
)

# 4. Set the gas price strategy
web3.eth.set_gas_price_strategy(rpc_gas_price_strategy)

# 5. Sign tx with PK
tx_create = web3.eth.account.sign_transaction(
    {
        "nonce": web3.eth.get_transaction_count(account_from["address"]),
        "gasPrice": web3.eth.generate_gas_price(),
        "gas": 21000,
        "to": address_to,
        "value": web3.toWei("1", "ether"),
    },
    account_from["private_key"],
)

# 6. Send tx and wait for receipt
tx_hash = web3.eth.send_raw_transaction(tx_create.rawTransaction)
tx_receipt = web3.eth.wait_for_transaction_receipt(tx_hash)

print(f"Transaction successful with hash: { tx_receipt.transactionHash.hex() }")

You can view the complete script on GitHub.

To run the script, you can run the following command in your terminal:

python3 transaction.py

If the transaction was succesful, in your terminal you'll see the transaction hash has been printed out.

You can also use the balances.py script to check that the balances for the origin and receiving accounts have changed. The entire workflow would look like this:

Send Tx Web3py

Deploy a Contract

The contract you'll be compiling and deploying in the next couple of sections is a simple incrementer contract, arbitrarily named Incrementer.sol. You can get started by creating a file for the contract:

touch Incrementer.sol

Next you can add the Solidity code to the file:

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

contract Incrementer {
    uint256 public number;

    constructor(uint256 _initialNumber) {
        number = _initialNumber;
    }

    function increment(uint256 _value) public {
        number = number + _value;
    }

    function reset() public {
        number = 0;
    }
}

The constructor function, which runs when the contract is deployed, sets the initial value of the number variable stored on-chain (default is 0). The increment function adds the _value provided to the current number, but a transaction needs to be sent, which modifies the stored data. Lastly, the reset function resets the stored value to zero.

Note

This contract is a simple example for illustration purposes only and does not handle values wrapping around.

Compile Contract Script

In this section, you'll create a script that uses the Solidity compiler to output the bytecode and interface (ABI) for the Incrementer.sol contract. To get started, you can create a compile.py file by running:

touch compile.py

Next, you will create the script for this file and complete the following steps:

  1. Import the solcx package
  2. Optional - If you haven't already installed the Solidity compiler, you can do so with by using the solcx.install_solc function
  3. Compile the Incrementer.sol function using the solcx.compile_files function
  4. Export the contract's ABI and bytecode
# 1. Import solcx
import solcx

# 2. If you haven't already installed the Solidity compiler, uncomment the following line
# solcx.install_solc()

# 3. Compile contract
temp_file = solcx.compile_files('Incrementer.sol')

# 4. Export contract data
abi = temp_file['Incrementer.sol:Incrementer']['abi']
bytecode = temp_file['Incrementer.sol:Incrementer']['bin']

Deploy Contract Script

With the script for compiling the Incrementer.sol contract in place, you can then use the results to send a signed transaction that deploys it. To do so, you can create a file for the deployment script called deploy.py:

touch deploy.py

Next, you will create the script for this file and complete the following steps:

  1. Import the ABI and bytecode
  2. Set up the Web3 provider
  3. Define the account_from, including the private_key. The private key is required to sign the transaction. Note: This is for example purposes only. Never store your private keys in a JavaScript file
  4. Create a contract instance using the web3.eth.contract function and passing in the ABI and bytecode of the contract
  5. Build a constructor transaction using the contract instance and passing in the value to increment by. For this example, you can use 5. You'll then use the buildTransaction function to pass in the transaction information including the from address and the nonce for the sender. To get the nonce you can use the web3.eth.get_transaction_count function
  6. Sign the transaction using the web3.eth.account.sign_transaction function and pass in the constructor transaction and the private_key of the sender
  7. Using the signed transaction, you can then send it using the web3.eth.send_raw_transaction function and wait for the transaction receipt by using the web3.eth.wait_for_transaction_receipt function
# 1. Import the ABI and bytecode
from compile import abi, bytecode

# 2. Add the Web3 provider logic here:
# {...}

# 3. Create address variable
account_from = {
    'private_key': 'YOUR-PRIVATE-KEY-HERE',
    'address': 'PUBLIC-ADDRESS-OF-PK-HERE',
}

print(f'Attempting to deploy from account: { account_from["address"] }')

# 4. Create contract instance
Incrementer = web3.eth.contract(abi=abi, bytecode=bytecode)

# 5. Build constructor tx
construct_txn = Incrementer.constructor(5).buildTransaction(
    {
        'from': account_from['address'],
        'nonce': web3.eth.get_transaction_count(account_from['address']),
    }
)

# 6. Sign tx with PK
tx_create = web3.eth.account.sign_transaction(construct_txn, account_from['private_key'])

# 7. Send tx and wait for receipt
tx_hash = web3.eth.send_raw_transaction(tx_create.rawTransaction)
tx_receipt = web3.eth.wait_for_transaction_receipt(tx_hash)

print(f'Contract deployed at address: { tx_receipt.contractAddress }')

You can view the complete script on GitHub.

To run the script, you can enter the following command into your terminal:

python3 deploy.py

If successful, the contract's address will be displayed in the terminal.

Deploy Contract Web3py

Read Contract Data (Call Methods)

Call methods are the type of interaction that don't modify the contract's storage (change variables), meaning no transaction needs to be sent. They simply read various storage variables of the deployed contract.

To get started, you can create a file and name it get.py:

touch get.py

Then you can take the following steps to create the script:

  1. Import the ABI
  2. Set up the Web3 provider
  3. Define the account_from, including the private_key. The private key is required to sign the transaction. Note: This is for example purposes only. Never store your private keys in a JavaScript file
  4. Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
  5. Using the contract instance, you can then call the number function
# 1. Import the ABI
from compile import abi

# 2. Add the Web3 provider logic here:
# {...}

# 3. Create address variable
contract_address = 'CONTRACT-ADDRESS-HERE'

print(f'Making a call to contract at address: { contract_address }')

# 4. Create contract instance
Incrementer = web3.eth.contract(address=contract_address, abi=abi)

# 5. Call Contract
number = Incrementer.functions.number().call()

print(f'The current number stored is: { number } ')

You can view the complete script on GitHub.

To run the script, you can enter the following command in your terminal:

python3 get.py

If successful, the value will be displayed in the terminal.

Interact with Contract (Send Methods)

Send methods are the type of interaction that modify the contract's storage (change variables), meaning a transaction needs to be signed and sent. In this section, you'll create two scripts: one to increment and one to reset the incrementer. To get started, you can create a file for each script and name them increment.py and reset.py:

touch increment.py reset.py

Open the increment.py file and take the following steps to create the script:

  1. Import the ABI
  2. Set up the Web3 provider
  3. Define the account_from, including the private_key, the contract_address of the deployed contract, and the value to increment by. The private key is required to sign the transaction. Note: This is for example purposes only. Never store your private keys in a JavaScript file
  4. Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
  5. Build the increment transaction using the contract instance and passing in the value to increment by. You'll then use the buildTransaction function to pass in the transaction information including the from address and the nonce for the sender. To get the nonce you can use the web3.eth.get_transaction_count function
  6. Sign the transaction using the web3.eth.account.sign_transaction function and pass in the increment transaction and the private_key of the sender
  7. Using the signed transaction, you can then send it using the web3.eth.send_raw_transaction function and wait for the transaction receipt by using the web3.eth.wait_for_transaction_receipt function
# 1. Import the ABI
from compile import abi

# 2. Add the Web3 provider logic here:
# {...}

# 3. Create variables
account_from = {
    'private_key': 'YOUR-PRIVATE-KEY-HERE',
    'address': 'PUBLIC-ADDRESS-OF-PK-HERE',
}
contract_address = 'CONTRACT-ADDRESS-HERE'
value = 3

print(
    f'Calling the increment by { value } function in contract at address: { contract_address }'
)

# 4. Create contract instance
Incrementer = web3.eth.contract(address=contract_address, abi=abi)

# 5. Build increment tx
increment_tx = Incrementer.functions.increment(value).buildTransaction(
    {
        'from': account_from['address'],
        'nonce': web3.eth.get_transaction_count(account_from['address']),
    }
)

# 6. Sign tx with PK
tx_create = web3.eth.account.sign_transaction(increment_tx, account_from['private_key'])

# 7. Send tx and wait for receipt
tx_hash = web3.eth.send_raw_transaction(tx_create.rawTransaction)
tx_receipt = web3.eth.wait_for_transaction_receipt(tx_hash)

print(f'Tx successful with hash: { tx_receipt.transactionHash.hex() }')

You can view the complete script on GitHub.

To run the script, you can enter the following command in your terminal:

python3 increment.py

If successful, the transaction hash will be displayed in the terminal. You can use the get.py script alongside the increment.py script to make sure that value is changing as expected:

Increment Contract Web3py

Next you can open the reset.py file and take the following steps to create the script:

  1. Import the ABI
  2. Set up the Web3 provider
  3. Define the account_from, including the private_key, and the contract_address of the deployed contract. The private key is required to sign the transaction. Note: This is for example purposes only. Never store your private keys in a JavaScript file
  4. Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
  5. Build the reset transaction using the contract instance. You'll then use the buildTransaction function to pass in the transaction information including the from address and the nonce for the sender. To get the nonce you can use the web3.eth.get_transaction_count function
  6. Sign the transaction using the web3.eth.account.sign_transaction function and pass in the reset transaction and the private_key of the sender
  7. Using the signed transaction, you can then send it using the web3.eth.send_raw_transaction function and wait for the transaction receipt by using the web3.eth.wait_for_transaction_receipt function
# 1. Import the ABI
from compile import abi

# 2. Add the Web3 provider logic here:
# {...}

# 3. Create variables
account_from = {
    'private_key': 'YOUR-PRIVATE-KEY-HERE',
    'address': 'PUBLIC-ADDRESS-OF-PK-HERE',
}
contract_address = 'CONTRACT-ADDRESS-HERE'

print(f'Calling the reset function in contract at address: { contract_address }')

# 4. Create contract instance
Incrementer = web3.eth.contract(address=contract_address, abi=abi)

# 5. Build reset tx
reset_tx = Incrementer.functions.reset().buildTransaction(
    {
        'from': account_from['address'],
        'nonce': web3.eth.get_transaction_count(account_from['address']),
    }
)

# 6. Sign tx with PK
tx_create = web3.eth.account.sign_transaction(reset_tx, account_from['private_key'])

# 7. Send tx and wait for receipt
tx_hash = web3.eth.send_raw_transaction(tx_create.rawTransaction)
tx_receipt = web3.eth.wait_for_transaction_receipt(tx_hash)

print(f'Tx successful with hash: { tx_receipt.transactionHash.hex() }')

You can view the complete script on GitHub.

To run the script, you can enter the following command in your terminal:

python3 reset.py

If successful, the transaction hash will be displayed in the terminal. You can use the get.py script alongside the reset.py script to make sure that value is changing as expected:

Reset Contract Web3py

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