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i have a problem and hope you could help me.

I try to swap BUSD on pancakeswap against an other token. I have a script, written in web3.py which works perfectly fine with BNB and the function "swapExactETHForTokens". But if i use the function: "swapExactTokensForTokens" I'm not in able to got a succesful transaction.

The script build the transaction, but after it is indexed by bscscan it failed.

Forexample: https://bscscan.com/tx/0xae08ebec2a945a727a8d5f158befa6baf943a7f149fad049eedb3f07908fe43a

I have tried to fix it the last days, but now i dont know further.

Her is the code:

import json
import config
import time
import sys

panabi = open('pancakeABI','r').read().replace('\n','')
sellABI = open('sellABI', 'r').read().replace('\n','')

bsc = "https://bsc-dataseed.binance.org/"
web3 = Web3(Web3.HTTPProvider(bsc))

print(web3.isConnected())

#TokenAddress of holder
sender_address = 'XXXXXX' 

#BUSD Address
spend = web3.toChecksumAddress("0x4Fabb145d64652a948d72533023f6E7A623C7C53")  


#pancakeswap router
panRouterContractAddress = '0x10ED43C718714eb63d5aA57B78B54704E256024E'

#Address Token
address = web3.toChecksumAddress(input("Token: "))

#Adddress Token
contract =  web3.eth.contract(address=address, abi=panabi)

#Balance
balance = web3.eth.get_balance(sender_address)
print(balance)
humanReadable = web3.fromWei(balance,'ether')
print(humanReadable)

#Setup contract pancake
contract = web3.eth.contract(address=panRouterContractAddress, abi=panabi)

nonce = web3.eth.get_transaction_count(sender_address)

start = time.time()
print(web3.toWei('0.02', 'ether'))


#Token instance
sellTokenContract = web3.eth.contract(address, abi=sellABI)


# 
tokenValue = web3.toWei(input("Enter amount you want to sell: "), 'ether')
int(tokenValue)

#Approve Token
tokenValue2 = web3.fromWei(tokenValue, 'ether')
start = time.time()
approve = sellTokenContract.functions.approve(panRouterContractAddress, tokenValue).buildTransaction({
    'from': sender_address,
    'gasPrice': web3.toWei('5','gwei'),
    'nonce': web3.eth.get_transaction_count(sender_address),
    })

signed_txn = web3.eth.account.sign_transaction(approve, private_key=config.private)
tx_token = web3.eth.send_raw_transaction(signed_txn.rawTransaction)
print("Approved: " + web3.toHex(tx_token))

time.sleep(7)

#build transaction
pancakeswap2_txn = contract.functions.swapExactTokensForTokens(
  tokenValue, # 
  1,
  [spend,address],
  sender_address,
  (int(time.time()) + 1000000)
).buildTransaction({
  'from': sender_address,
  # 'value': web3.toWei(0,'ether'),
  'gas': 500000,
  'gasPrice': web3.toWei('10','gwei'),
  'nonce': nonce,
})

#sign transaction
signed_txn = web3.eth.account.sign_transaction(pancakeswap2_txn, private_key=config.private)
tx_token = web3.eth.send_raw_transaction(signed_txn.rawTransaction)
print(web3.toHex(tx_token))

#Wait for transaction receipt

print("Wait...")
time.sleep(5)
receipt = web3.eth.wait_for_transaction_receipt(tx_token, timeout=300, poll_latency=0.1)
print(receipt)```

Thank you in advance.

1 Answer 1

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this might solve your issue. first, instead of passing 1 as a number into the output amount, the router contract has a public function that you can use to get the exact output amount and the result can be passed into where you need to put the output amount.

here:

function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);

for the failed transaction from what I found out here: https://bscscan.com/vmtrace?txhash=0xae08ebec2a945a727a8d5f158befa6baf943a7f149fad049eedb3f07908fe43a&type=gethtrace2 you can increase the amount of gas or use the getgasPrice from web3.py.

Also the function you are calling doesn't require you to pass in value, here:

 function swapExactTokensForTokens(
    uint amountIn,
    uint amountOutMin,
    address[] calldata path,
    address to,
    uint deadline
) external returns (uint[] memory amounts);

as require first is -input amount

  • output amount (you can use the getAmountsOut() for that)

  • [busd address(which is the token to swap note you must approve this first), token to get address]

  • recipient address

  • deadline

    pancakeswap2_txn = contract.functions.swapExactTokensForTokens( busd amount (Note: must be approved), getAmountOut, [busd address, token to get address], sender_address, (int(time.time()) + 1000000) ).buildTransaction({ 'from': sender_address, 'gas': 500000, 'gasPrice': web3.toWei('10','gwei'), 'nonce': nonce,

hope this help.

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