Web3.py

Web3.py Python Library

Introduction

Web3.py is a set of libraries that allow developers to interact with Ethereum nodes using HTTP, IPC, or WebSocket protocols with Python. Phron 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 Phron 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 Phron.

Checking Prerequisites

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

An account with funds. You can get DEV tokens for testing on Phron once every 24 hours from the Phron Faucet
To test out the examples in this guide on Phron, 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 assume you have a MacOS or Ubuntu 22.04-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 solc-select

Setup Web3.py with Phron

Throughout this guide, you'll be creating a bunch of scripts that provide different functionalities, such as sending a transaction, deploying a contract, and interacting with a deployed contract. In most of these scripts, you'll need to create a Web3.py provider to interact with the network.

To configure your project for Phron, you will need to have your own endpoint and API key, which you can get from one of the supported Endpoint Providers.

To create a provider, you can take the following steps:

Import the web3 library
Create the web3 provider using the Web3(Web3.HTTPProvider()) method and providing the endpoint URL

# 1. Import web3.py
from web3 import Web3

# 2. Create web3.py provider
web3 = Web3(Web3.HTTPProvider("INSERT_RPC_API_ENDPOINT")) # Insert your RPC URL here

Save this code snippet, as you'll need it for the scripts that are used in the following sections.

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:

Set up the Web3 provider
Define the address_from and address_to variables
Get the balance for the accounts using the web3.eth.get_balance function and format the results using the web3.from_wei

from web3 import Web3

# 1. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 2. Create address variables
address_from = 'INSERT_FROM_ADDRESS'
address_to = 'INSERT_TO_ADDRESS'

# 3. Fetch balance data
balance_from = web3.from_wei(
    web3.eth.get_balance(Web3.to_checksum_address(address_from)), "ether"
)
balance_to = web3.from_wei(
    web3.eth.get_balance(Web3.to_checksum_address(address_to)), "ether"
)

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

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:

Add imports, including Web3.py and the rpc_gas_price_strategy, which will be used in the following steps to get the gas price used for the transaction
Set up the Web3 provider
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 Python file
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
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.to_wei function
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. Add imports
from web3.gas_strategies.rpc import rpc_gas_price_strategy
from web3 import Web3

# 2. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 3. Create address variables
account_from = {
    'private_key': 'INSERT_YOUR_PRIVATE_KEY',
    'address': 'INSERT_PUBLIC_ADDRESS_OF_PK',
}
address_to = 'INSERT_TO_ADDRESS'

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(
            Web3.to_checksum_address(account_from["address"])
        ),
        "gasPrice": web3.eth.generate_gas_price(),
        "gas": 21000,
        "to": Web3.to_checksum_address(address_to),
        "value": web3.to_wei("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() }")

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:

python3 balances.pyThe balance of 0x3B939FeaD1557C741Ff06492FD0127bd287A421e is: 3563.79 DEVThe balance of 0x9Bf5Ae10540a1ab9B363bEA02A9406E6b2efA9af is: 0 DEVpython3 transaction.pyAttempting to send transaction from 0x3B939FeaD1557C741Ff06492FD0127bd287A421e to 0x9Bf5Ae10540a1ab9B363bEA02A9406E6b2efA9afTransaction successful with hash: 0xac70452510657ed43c27510578d3ce4b3b880d4cca1a24ade1497c6e0ee7f5d6python3 balances.pyThe balance of 0x3B939FeaD1557C741Ff06492FD0127bd287A421e is: 3562.79 DEVThe balance of 0x9Bf5Ae10540a1ab9B363bEA02A9406E6b2efA9af is: 1 DEV

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 (the 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:

Import the solcx package
Optional - If you haven't already installed the Solidity compiler, you can do so with by using the solcx.install_solc function
Compile the Incrementer.sol function using the solcx.compile_files function
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',
    output_values=['abi', 'bin'],
    # solc_version='0.8.19'
)

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

Note
If you see an error stating that Solc is not installed, uncomment step 2 described in the code snippet.

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:

Add imports, including Web3.py and the ABI and bytecode of the Incrementer.sol contract
Set up the Web3 provider
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 Python file
Create a contract instance using the web3.eth.contract function and passing in the ABI and bytecode of the contract
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 build_transaction 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
Sign the transaction using the web3.eth.account.sign_transaction function and pass in the constructor transaction and the private_key of the sender
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. Add imports
from compile import abi, bytecode
from web3 import Web3

# 2. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 3. Create address variable
account_from = {
    'private_key': 'INSERT_YOUR_PRIVATE_KEY',
    'address': 'INSERT_PUBLIC_ADDRESS_OF_PK',
}

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).build_transaction(
    {
        "from": Web3.to_checksum_address(account_from["address"]),
        "nonce": web3.eth.get_transaction_count(
            Web3.to_checksum_address(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 }")

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.

python3 deploy.pyAttempting to deploy from account: 0x3B939FeaD1557C741Ff06492FD0127bd287A421eContract deployed at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08

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:

Add imports, including Web3.py and the ABI of the Incrementer.sol contract
Set up the Web3 provider
Define the contract_address of the deployed contract
Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
Using the contract instance, you can then call the number function

# 1. Import the ABI
from compile import abi
from web3 import Web3

# 2. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 3. Create address variable
contract_address = 'INSERT_CONTRACT_ADDRESS'

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 } ")

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:

Add imports, including Web3.py and the ABI of the Incrementer.sol contract
Set up the Web3 provider
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 Python file
Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
Build the increment transaction using the contract instance and passing in the value to increment by. You'll then use the build_transaction 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
Sign the transaction using the web3.eth.account.sign_transaction function and pass in the increment transaction and the private_key of the sender
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. Add imports
from compile import abi
from web3 import Web3

# 2. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 3. Create variables
account_from = {
    'private_key': 'INSERT_YOUR_PRIVATE_KEY',
    'address': 'INSERT_PUBLIC_ADDRESS_OF_PK',
}
contract_address = 'INSERT_CONTRACT_ADDRESS'
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).build_transaction(
    {
        "from": Web3.to_checksum_address(account_from["address"]),
        "nonce": web3.eth.get_transaction_count(
            Web3.to_checksum_address(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() }")

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:

python get.pyMaking a call to contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08The current number stored is: 5python increment.pyCalling the increment by 3 function in contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08Tx successful with hash: 0x47757fd97e3ef8db973e335d1f2d19c46b37d0dbd53fea1636ec559ccf119a13python get.pyMaking a call to contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08The current number stored is: 8

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

Add imports, including Web3.py and the ABI of the Incrementer.sol contract
Set up the Web3 provider
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 Python file
Create a contract instance using the web3.eth.contract function and passing in the ABI and address of the deployed contract
Build the reset transaction using the contract instance. You'll then use the build_transaction 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
Sign the transaction using the web3.eth.account.sign_transaction function and pass in the reset transaction and the private_key of the sender
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. Add imports
from compile import abi
from web3 import Web3

# 2. Add the Web3 provider logic here:
provider_rpc = {
    "development": "http://localhost:9944",
    "phron": "https://testnet.phron.ai",
}
web3 = Web3(Web3.HTTPProvider(provider_rpc["phron"]))  # Change to correct network

# 3. Create variables
account_from = {
    'private_key': 'INSERT_YOUR_PRIVATE_KEY',
    'address': 'INSERT_PUBLIC_ADDRESS_OF_PK',
}
contract_address = 'INSERT_CONTRACT_ADDRESS'

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().build_transaction(
    {
        "from": Web3.to_checksum_address(account_from["address"]),
        "nonce": web3.eth.get_transaction_count(
            Web3.to_checksum_address(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() }")

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:

python get.pyMaking a call to contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08The current number stored is: 8python reset.pyCalling the reset function in contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08Tx successful with hash: 0x152f07430b524838da848b44d58577db252681fba6fbeaf117b2f9d432e301b2python get.pyMaking a call to contract at address: 0xFef3cFb8eE1FE727b3848E551ae5DC8903237B08The current number stored is: 0

This tutorial is for educational purposes only. As such, any contracts or code created in this tutorial should not be used in production.The information presented herein has been provided by third parties and is made available solely for general information purposes. Phron does not endorse any project listed and described on the Phron Doc Website (https://docs.Phron.ai/). Phron does not warrant the accuracy, completeness or usefulness of this information. Any reliance you place on such information is strictly at your own risk. Phron disclaims all liability and responsibility arising from any reliance placed on this information by you or by anyone who may be informed of any of its contents. All statements and/or opinions expressed in these materials are solely the responsibility of the person or entity providing those materials and do not necessarily represent the opinion of Phron. The information should not be construed as professional or financial advice of any kind. Advice from a suitably qualified professional should always be sought in relation to any particular matter or circumstance. The information herein may link to or integrate with other websites operated or content provided by third parties, and such other websites may link to this website. Phron has no control over any such other websites or their content and will have no liability arising out of or related to such websites or their content. The existence of any such link does not constitute an endorsement of such websites, the content of the websites, or the operators of the websites. These links are being provided to you only as a convenience and you release and hold Phron harmless from any and all liability arising from your use of this information or the information provided by any third-party website or service.

Last updated 9 months ago