Web3.py ABI – How to Call Smart Contract Functions Without the ABI

Here's a database of mappings from the functions to the function signatures - https://www.4byte.directory/. Note that the server has been returning 'Server Error (500)' intermittently.

Some further information about this service: Ethereum Function Signature Database - database of 4-Btye function signatures to their human readable counterparts.

The documentation is skimpy on details and it took me forever to figure out the correct way with the help of your links, anyways, here is what works for me:

Tested on Geth : 1.6.7 -stable , web3.js :0.20.2 Parity/v1.7.2 & Kovan testnet.

I'll be using the minimal token as example :

pragma solidity ^0.4.0;

contract minimalToken {

     mapping (address => uint256) public balanceOf;

    function minimalToken(uint256 initialSupply) {
        balanceOf[msg.sender] = initialSupply;
    }

    function transfer(address _to, uint256 _value) {
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        balanceOf[msg.sender] -= _value;
        balanceOf[_to] += _value;
    }
}

I'll be focusing on the transfer method which takes 2 arguments,( address, amount) to transfer:

    var contract = web3.eth.contract(contractABI).at("0x8caaa1f263ff14d0276ff1a1a6ed15c51159d6e0");
    var receiverAddress = '0x00Ce6C92856A657979E7728005DBc9acD002Eb09';
    var callData = contract.transfer.getData(receiverAddress, 2000);

    var gasEstimate = web3.eth.estimateGas({
        from: web3.eth.coinbase,
        to: "0x8caaa1f263ff14d0276ff1a1a6ed15c51159d6e0",
        data: callData
    });

    var gasPrice = web3.eth.gasPrice;

    console.log('gas Price: ' + gasPrice);
    console.log('Estimated Transaction gas: ' + gasEstimate);

// gas Price: 21000000000
// Estimated Transaction gas: 34207

One thing that Threw me off, was that I kept on getting transaction errors due to me not including the from: field on the transaction.

Hope this helps.