[Ethereum] web3 py – transact call with struct parameter

I am trying to call a smart constract function with the following abi with pragma experimental ABIEncoderV2:

        "constant": false,
        "inputs": [
            {
                "name": "blockNumber",
                "type": "uint256"
            },
            {
                "name": "data",
                "type": "bytes"
            },
            {
                "name": "tokenNum",
                "type": "uint256"
            }
        ],
        "name": "execute",
        "outputs": [],
        "payable": false,
        "stateMutability": "nonpayable",
        "type": "function"

The data parameter is a struct with the following definition in solidity

struct InputParams {
        address addressFirst;
        address addressSecond;
        uint256 tokenAmount;
    }

How can I encode the data on the python side? I am getting error

Could not identify the intended function with name `execute`, positional argument(s) of type `(<class 'int'>, <class 'list'>, <class 'int'>)` and keyword argument(s) of type `{}`. Found 1 function(s) with the name `execute`: ['execute(uint256,bytes,uint256)']

I think I need to convert the python list into 'bytes' type, but how do I specify in the bytes that necessary datatypes of the struct?