I am trying to sell my tokens via python web3. But sometimes I get an error "execution reverted: Pancake: K". I researched this error and it has to do with the slippage but pancake swap docs tell me a slippage option is on their site. But I want to sell this token via python. How can I add a slippage tolerance option?

This is my web3.py code:

spend = web3.toChecksumAddress("0xbb4cdb9cbd36b01bd1cbaebf2de08d9173bc095c")
balance = web3.eth.get_balance(sender_address)
humanReadable = web3.fromWei(balance, 'ether')
contract_id = web3.toChecksumAddress(contractaddress)
sellTokenContract = web3.eth.contract(contract_id, abi=sellAbi)
balance = sellTokenContract.functions.balanceOf(sender_address).call()
symbol = sellTokenContract.functions.symbol().call()
readable = web3.fromWei(balance, 'ether')
    tokenValue = web3.toWei(readable, 'ether')
    tokenValue2 = web3.fromWei(tokenValue, 'ether')
    start = time.time()
    approve = sellTokenContract.functions.approve(panRouterContractAddress, balance).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))
    print(f"Swapping {tokenValue2} {symbol} for BNB")

    pancakeswap2_txn = contract.functions.swapExactTokensForETHSupportingFeeOnTransferTokens(
        (int(time.time()) + 10000)
        'from': sender_address,
        'gasPrice': web3.toWei(str(gwei), 'gwei'),
        'nonce': web3.eth.get_transaction_count(sender_address),


    signed_txn = web3.eth.account.sign_transaction(pancakeswap2_txn, private_key=config.private)
    tx_token = web3.eth.send_raw_transaction(signed_txn.rawTransaction)
    print(f"Sold {symbol}: " + web3.toHex(tx_token))

1 Answer 1


A slippage tolerance option is already added to your code.

In the func

swapExactTokensForETHSupportingFeeOnTransferTokens(amountIn, amountOutMin, path, to, deadline)

amountOutMin is yout slippage tolerance.

When amountOutMin equals 0 it means you will find the best price and execute transaction. If you specify amountOutMin for some number and price will go under your number -> transaction cancels.

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