Ethereum Smart Function Call Not Working: Python vs Truffle Dev

As a developer building decentralized applications (dApps) on the Ethereum network using smart contracts, you’re probably no stranger to the complexities of interacting with the blockchain. However, when it comes to calling specific functions from external scripts, errors can be frustrating and difficult to troubleshoot.

In this article, we’ll explore why a call to the AddDeviceOwner function might not work as expected in a Python script, despite being successful in the Truffle Dev console environment.

The Problem

Let’s say you have a smart contract deployed on Ethereum that defines an AddDeviceOwner function. You want to write a Python script to call this function and test its functionality. Here’s what happens when you try to run the code:

import web3

Assuming w3 is your Web3 instance
w3 = web3.Web3()

Deploying the contract (replace with your actual deployment logic)
contract = w3.eth.contract(address="0x...", abi={"function": "AddDeviceOwner"}) 
Replace with your contract code

The AddDeviceOwner function takes two parameters: owner and newOwner. When you call this function in Truffle Dev, it should execute fine. However, if something is missing from your Python script, you will not see any errors or warnings. The function simply returns nothing.

The Problem

In your Python code, you are trying to access the contract instance with w3 = web3.Web3() and then trying to call the AddDeviceOwner function with contract = w3.eth.contract(address="0x...", abi={"function": "AddDeviceOwner"}). However, because the Truffle Dev environment has already deployed the contract to the testnet, it does not have any instances of the smart contract. Therefore, attempting to create a new instance using w3 is futile and will result in an error.

Solution

To resolve this issue, you need to modify your Python script to use Truffle Dev’s deployment logic instead of creating a new contract instance. Here’s how:

import web3

Importing libraries required by Truffle
from truffle.test import TestProvider
from contract import Contract 
Replace with your actual contract code

Set up the Truffle Dev provider
test_provider = Test_provider()

Deploying the contract (replace with your actual deployment logic)
contract = Contract.from_abi("path/to/your/contract.abi", test_provider, "0x...", {"function": "AddDeviceOwner"}) 
Replace with your contract code

Now you can call the AddDeviceOwner function
result = contract.addDeviceOwner("owner", "newOwner")
print(result)

In this revised script, we import the TestProvider class from the Truffle library and the we use to deploy the contract. The resulting contract instance is then used to call the AddDeviceOwner function.

Additional tips

To first ensure that your smart contracts deploy correctly, you should:

• Use the correct ABI (Application Binary Interface) for your contract.

• Configure a Truffle Dev provider with the correct settings for your local network or testnet.

• Deploy the contract using a tool such as Truffle’s truffle deploy command.

By following these steps and modifying your Python script to use Truffle Dev’s deployment logic, you should be able to successfully invoke smart function calls from your Python scripts, even if they don’t work in the Truffle Dev console environment.