Smart Contract – approve function: wad

blockchainweb3.py

In context of "Approve" function in smart contract https://cronos.org/explorer/address/0x66e428c3f67a68878562e79A0234c1F83c208770/contracts

function approve(address guy, uint wad) public stoppable returns (bool)

What's "Wad"? From the reference, apparently, it's an 18 digits number. Ok. But is it in Gwei and Wei ..etc?

Thanks

Similar question, what's estimate_gas returning? Gwei or Wei?

Best Answer

So web3 interpret "wad" as "wei".

from web3 import Web3

my_wallet_address = "xxx"
wallet_address = Web3.toChecksumAddress(my_wallet_address)
private_key = "xxx_tellme_xxx"

EIP20_ABI = '[{"constant":true,"inputs":[],"name":"name","outputs":[{"name":"","type":"string"}],"payable":false,"stateMutability":"view","type":"function"},{"constant":false,"inputs":[{"name":"_spender","type":"address"},{"name":"_value","type":"uint256"}],"name":"approve","outputs":[{"name":"","type":"bool"}],"payable":false,"stateMutability":"nonpayable","type":"function"} ... blah ...]' 

wcro_address = Web3.toChecksumAddress("0x5C7F8A570d578ED84E63fdFA7b1eE72dEae1AE23")
wcro_contract = w3.eth.contract(address=wcro_address, abi=EIP20_ABI)

ONE_BILLION : int = 1000000000
approval_amount_in_usdt : int = 100
cro_usdt = 0.42 # rate on 20220413
approval_amount_in_cro : int = int(approval_amount_in_usdt * cro_usdt)

default_gas_limit = 800_000
gas_price = w3.eth.gasPrice
'''
If you're interacting with CRONOS chain, 
    allowance_amount_in_wei = approval_amount_in_cro * ONE_BILLION * ONE_BILLION
If you're interacting with Etherum chain,
    allowance_amount_in_wei = approval_amount_in_eth * ONE_BILLION * ONE_BILLION
'''
allowance_amount_in_wei = approval_amount_in_cro * ONE_BILLION * ONE_BILLION

approval_transaction = wcro_contract.functions.approve( # If you want to swap USDT to SINGLE, change here.
    router_address,
    allowance_amount_in_wei,
)
nonce = w3.eth.getTransactionCount(wallet_address)
approval_trx_params = approval_transaction.buildTransaction({
    'from': wallet_address,
    'gas': default_gas_limit,  # here we use the default gas limit. See the swap trx below for estimated gas
    'gasPrice': gas_price,
    'nonce': nonce,
})
signed = w3.eth.account.sign_transaction(approval_trx_params, private_key)
approval_trx_hash = w3.eth.sendRawTransaction(signed.rawTransaction)
receipt = w3.eth.waitForTransactionReceipt(approval_trx_hash)
assert receipt["status"] == 1  # trx success
assert wcro_contract.functions.allowance(wallet_address, router_address).call() == allowance_amount_in_wei

References:

https://www.thebalance.com/gwei-5194614

https://norman-lm-fung.medium.com/interact-with-cronos-single-usdc-lp-with-web3-py-1e14c62a0d9c

Related Solutions

[Ethereum] Call Smart Contract Function in Python Script

Here is an example using Brownie that should help:

import time
from brownie import Contract, network, web3


abi = {}          # contract ABI as a dict
address = "0x00"  # contract address as a string


network.connect('mainnet')
my_contract = Contract("MyContractName", address, abi=abi)

height = web3.eth.blockNumber

while True:
    result = my_contract.myCallableFn(arg1, arg2) # change to call the desired method
    if result == desired_result:
        # do whatever you need to do

    while web3.eth.blockNumber == height:
        time.sleep(1)
    height = web3.eth.blockNumber

You will have to modify some configuration settings to point at your own node, or set an infura API key in your environment variables.

The documentation on accessing contract methods might also be useful if my example is unclear.

Hope this helps.

[Ethereum] Execute smart contract function on python

The relevant piece of documentation is here

You'll need to get the contract ABI from somewhere, either by having it from when you deployed, or using a different tool. Once you have that, you can use web3.py to load it:

store_var_contract = w3.eth.contract(
   address=address,
   abi=contract_interface['abi'])

You can then call the function in the contract using the variable you assigned the contract. The example in the docs includes how to estimate the gas and more.

So, if you load your contract using the snippet above, and you want to call a function withdrawToken(), you could then use something like:

tx_hash = store_var_contract.functions.withdrawToken(0x..., 50).transact()
receipt = w3.eth.waitForTransactionReceipt(tx_hash)

Where 0x... is the address you wanted, and 50 is a random number I picked for the amount, and should be replaced by a number of your choice. (Unless you coincidentally wanted 50.)

I'm going out on a limb here, but I have a suspicion part of the issue may be that you've already deployed the contract, and don't have its ABI. A few quick solutions may include using the Solidity compiler to get the ABI (solc --abi YourContract.sol if you already have it installed), or if you know where an identical contract is deployed on a test chain or mainnet, getting its ABI from etherscan.

Best Answer

Related Solutions

[Ethereum] Call Smart Contract Function in Python Script

[Ethereum] Execute smart contract function on python

Related Topic