使用 web3.py 解码智能合约的返回值？

Question

I'm reposting the question since it wasn't well describe.

I'm working on a smart contract that is suppose to return 1 when I call it with a python script using web3.py, but instead of having a 1 in my python scirpt I receive an hexbytes object. I suppose I need to decode it using the ABI and web3.py but I don't know how?

I have a function like this in solidity:

pragma solidity ^0.5.10;

contract test {
    function test(int a) public returns (int) {
            if(a > 0){
                return 1;
            }
        }
}

When I called it with my python script:

import json

import web3
from web3 import Web3

#To connect to ganache blockchain:
ganache_url = "http://127.0.0.1:7545"
web3 = Web3(Web3.HTTPProvider(ganache_url))

#this script will be the account number 1 on ganache blockchain:
web3.eth.defaultAccount = web3.eth.accounts[1]

#smart contract: abi, address and bytecode
abi = json.loads('....')
address = web3.toChecksumAddress("0x4A4AaA64857aa08a709A3470A016a516d3da40bf")
bytecode = "..."

#refering to the deploy coontract
contract = web3.eth.contract(address = address, abi = abi, bytecode = bytecode)

con = contract.functions.test(52).transact()
print(con.hex())

I have result like this:

<class 'hexbytes.main.HexBytes'>
0x3791e76f3c1244722e60f72ac062765fca0c00c25ac8d5fcb22c5a9637c3706d

Can someone help?

Answer 1

The transact() method submits the transaction and returns transaction hash. You should first wait for the transaction to be mined, and get the transaction receipt using w3.eth.waitForTransactionReceipt . If you intend to use a transaction instead of a call you can get the result of your function by mutating the state and then reading the resulting state by calling a view function or mutating the state and generating an event .

In your case you don't mutate the state so you can mark your function as view :

function test(int a) view public returns (int)

and then use call instead of generating a transaction:

contract.functions.test(52).call()

You can read here about the difference between a transaction and a call .

Also the official web3py documentation has many examples of invoking smart contract functions.