How to send ERC20 token to another account using web3.py, rinkeby and infura

Question

I built an ERC20 token with smart contract. It's AZ Token. I have a problem with building transaction from the account that has the total supply to another account Here is the source code and below, i mentioned what i get as a response Please note that i removed the real private key

    import json

from web3 import Web3
from solcx import compile_standard, install_solc
import os

import web3
import os
from eth_account import Account
from eth_account.signers.local import LocalAccount
from web3.auto import w3
from web3.middleware import construct_sign_and_send_raw_middleware
with open("./Token.sol", "r") as file:
    simple_storage_file = file.read()
compiled_sol = compile_standard(
    {
        "language": "Solidity",
        "sources": {"Token.sol": {"content": simple_storage_file}},
        "settings": {
            "outputSelection": {
                "*": {
                    "*": ["abi", "metadata", "evm.bytecode", "evm.bytecode.sourceMap"]
                }
            }
        },
    },
    solc_version="0.5.0",
)
ABI = compiled_sol["contracts"]["Token.sol"]["AZ"]["abi"]
w3 = Web3(Web3.HTTPProvider('https://eth-rinkeby.alchemyapi.io/v2/s1IuFuwxKv-xgoGblVYDNVmbegeiqCLB'))


unicorns = w3.eth.contract(address="0x5c5ABbfEdC882D7D863F9EF41d5CF6FF928aCf66", abi=ABI)
nonce = w3.eth.get_transaction_count('0xF56A9A5c8fcBC092b8881e9f34B5ea0e6881C865')
unicorn_txn = unicorns.functions.transfer(
    '0x0cfb925C00a4CEF8a22a9F72BC27cCDF074E542C',
    900000000000000000000,
).buildTransaction({
    'chainId': 4,
    'gas': 70000,
    'maxFeePerGas': w3.toWei('90', 'gwei'),
    'maxPriorityFeePerGas': w3.toWei('90', 'gwei'),
    'nonce': nonce+1,
})
private_key = '0x241234123512341234'
signed_txn = w3.eth.account.sign_transaction(unicorn_txn, private_key=private_key)
tx_greeting_hash = w3.eth.send_raw_transaction(signed_txn.rawTransaction)

This is what i get:

This is the source code of the contract:

    /**
 *Submitted for verification at Etherscan.io on 2022-06-23
*/

pragma solidity ^0.5.0;

// ----------------------------------------------------------------------------
// ERC Token Standard #20 Interface
//
// ----------------------------------------------------------------------------
contract ERC20Interface {
    function totalSupply() public view returns (uint);
    function balanceOf(address tokenOwner) public view returns (uint balance);
    function allowance(address tokenOwner, address spender) public view returns (uint remaining);
    function transfer(address to, uint tokens) public returns (bool success);
    function approve(address spender, uint tokens) public returns (bool success);
    function transferFrom(address from, address to, uint tokens) public returns (bool success);

    event Transfer(address indexed from, address indexed to, uint tokens);
    event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}

// ----------------------------------------------------------------------------
// Safe Math Library
// ----------------------------------------------------------------------------
contract SafeMath {
    function safeAdd(uint a, uint b) public pure returns (uint c) {
        c = a + b;
        require(c >= a);
    }
    function safeSub(uint a, uint b) public pure returns (uint c) {
        require(b <= a); c = a - b; } function safeMul(uint a, uint b) public pure returns (uint c) { c = a * b; require(a == 0 || c / a == b); } function safeDiv(uint a, uint b) public pure returns (uint c) { require(b > 0);
        c = a / b;
    }
}


contract AZ is ERC20Interface, SafeMath {
    string public name;
    string public symbol;
    uint8 public decimals; // 18 decimals is the strongly suggested default, avoid changing it

    uint256 public _totalSupply;

    mapping(address => uint) balances;
    mapping(address => mapping(address => uint)) allowed;

    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor() public {
        name = "AZ Token";
        symbol = "AZ";
        decimals = 18;
        _totalSupply = 100000000 *(10**18);

        balances[msg.sender] = _totalSupply;
        emit Transfer(address(0), msg.sender, _totalSupply);
    }

    function totalSupply() public view returns (uint) {
        return _totalSupply  - balances[address(0)];
    }

    function balanceOf(address tokenOwner) public view returns (uint balance) {
        return balances[tokenOwner];
    }

    function allowance(address tokenOwner, address spender) public view returns (uint remaining) {
        return allowed[tokenOwner][spender];
    }

    function approve(address spender, uint tokens) public returns (bool success) {
        allowed[msg.sender][spender] = tokens;
        emit Approval(msg.sender, spender, tokens);
        return true;
    }

    function transfer(address to, uint tokens) public returns (bool success) {
        balances[msg.sender] = safeSub(balances[msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(msg.sender, to, tokens);
        return true;
    }

    function transferFrom(address from, address to, uint tokens) public returns (bool success) {
        balances[from] = safeSub(balances[from], tokens);
        allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
        balances[to] = safeAdd(balances[to], tokens);
        emit Transfer(from, to, tokens);
        return true;
    }
}

Answer 1

Here is a tutorial on how to transfer ERC-20 tokens using web3.py. It is using web3-ethereum-defi library for token helpers.

import datetime
import os
import sys
from decimal import Decimal

from eth_account import Account
from eth_account.signers.local import LocalAccount
from web3 import HTTPProvider, Web3
from web3.middleware import construct_sign_and_send_raw_middleware

from eth_defi.abi import get_deployed_contract
from eth_defi.token import fetch_erc20_details
from eth_defi.txmonitor import wait_transactions_to_complete

# What is the token we are transferring.
# Replace with your own token address.
ERC_20_TOKEN_ADDRESS = "0x0aC7B3733cBeE5D87A80fbf331f4A0bD01f17386"

# Connect to JSON-RPC node
json_rpc_url = os.environ["JSON_RPC_URL"]
web3 = Web3(HTTPProvider(json_rpc_url))
print(f"Connected to blockchain, chain id is {web3.eth.chain_id}. the latest block is {web3.eth.block_number:,}")

# Read and setup a local private key
private_key = os.environ.get("PRIVATE_KEY")
assert private_key is not None, "You must set PRIVATE_KEY environment variable"
assert private_key.startswith("0x"), "Private key must start with 0x hex prefix"
account: LocalAccount = Account.from_key(private_key)
web3.middleware_onion.add(construct_sign_and_send_raw_middleware(account))

# Show users the current status of token and his address
erc_20 = get_deployed_contract(web3, "ERC20MockDecimals.json", ERC_20_TOKEN_ADDRESS)
token_details = fetch_erc20_details(web3, ERC_20_TOKEN_ADDRESS)

print(f"Token details are {token_details}")

balance = erc_20.functions.balanceOf(account.address).call()
eth_balance = web3.eth.getBalance(account.address)

print(f"Your balance is: {token_details.convert_to_decimals(balance)} {token_details.symbol}")
print(f"Your have {eth_balance/(10**18)} ETH for gas fees")

# Ask for transfer details
decimal_amount = input("How many tokens to transfer? ")
to_address = input("Give destination Ethereum address? ")

# Some input validation
try:
    decimal_amount = Decimal(decimal_amount)
except ValueError as e:
    raise AssertionError(f"Not a good decimal amount: {decimal_amount}") from e

assert web3.isChecksumAddress(to_address), f"Not a valid address: {to_address}"

# Fat-fingering check
print(f"Confirm transfering {decimal_amount} {token_details.symbol} to {to_address}")
confirm = input("Ok [y/n]?")
if not confirm.lower().startswith("y"):
    print("Aborted")
    sys.exit(1)

# Convert a human-readable number to fixed decimal with 18 decimal places
raw_amount = token_details.convert_to_raw(decimal_amount)
tx_hash = erc_20.functions.transfer(to_address, raw_amount).transact({"from": account.address})

# This will raise an exception if we do not confirm within the timeout
print(f"Broadcasted transaction {tx_hash.hex()}, now waiting 5 minutes for mining")
wait_transactions_to_complete(web3, [tx_hash], max_timeout=datetime.timedelta(minutes=5))

print("All ok!")