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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?

user3761555
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1 Answers1

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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

user3761555
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