Web3.py – Making an ERC20 Transfer Using Python

erc-20pythontransferweb3.py

how to send an erc20 in web3py please, I have that :

tx_hash = contract.functions.transfer(destination_address, value).transact({'from': myaddress })

and I get this error :

ValueError: {'code': -32601, 'message': 'The method eth_sendTransaction does not exist/is not available'}

I guess am missing signing that or something like that, how can I make a successful erc20 transfer.

Best Answer

transact() asks the node to sign your transaction using eth_sendTransaction. Infura can't do that, because they don't have your keys.

Instead, you can use the contract object to create an unsigned transaction like:

contract_call = contract.functions.transfer(destination_address, value)
unsigned_txn = contract_call.buildTransaction({'chainId': 1, 'gasPrice': w3.toWei(100, 'gwei')})

Then you can sign the transaction with your private key, and broadcast it:

signed_txn = w3.eth.account.sign_transaction(unsigned_txn, private_key=private_key)
w3.eth.sendRawTransaction(signed_txn.rawTransaction)

Related Solutions

Web3.py – Signing a Raw Transaction on Contract Function

The problem is that the transaction sets a chainId of 10, but the genesis file does not specify chainId.

A mismatched chainId will cause a failure in your node (which is supposed to happen, that's how the node prevents transaction replays).

If your node does not support chainId in the genesis file (which populus may not), then setting chainId to None in the transaction is the correct solution.

However, if you are using geth, you can set the chainId in the genesis file, like so:

{
"parentHash":  "0x0000000000000000000000000000000000000000000000000000000000000000",
"coinbase": "0xf2419003e9058198c71e42bb35f94b4452fadfa8",
"extraData": "0x686f727365",
"config": {
  "chainId": 10,
  "daoForkBlock": 0,
  "daoForSupport": true,
  "homesteadBlock": 0
},
"timestamp": "0x0",
"mixhash":  "0x0000000000000000000000000000000000000000000000000000000000000000",
"nonce": "0xdeadbeefdeadbeef",
"alloc": {
  "0x3d48e3a6a661e5dc56db193e49d484e79c927652": {
    "balance": "1000000000000000000000000000000"
  }
},
"gasLimit": "0x3b62df92707000",
"difficulty": "0x01"
}

[Ethereum] How much gas does an ERC20 transfer cost

The only thing you can definitely tell is that it will not be below 21.000, which is the minimum transaction cost, and that it will not be above the gasLimit of the block. Everything else depends on the implementation of the contract. The average of existing tokens can be calculated based on block/tx data.

Moreover, you can dry run your transaction against your local node to get a pretty good estimate how much the transaction will cost.

Best Answer

Related Solutions

Web3.py – Signing a Raw Transaction on Contract Function

[Ethereum] How much gas does an ERC20 transfer cost

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