Python – How to Call a Deployed Smart Contract on Kovan Using Web3.py

contract-invocationkovanpythonremixweb3.py

The smart contract was written and deployed on Kovan using Remix IDE and injected Metamask Kovan test network account. However, I'll need python to deal with large input of a function in the smart contract. How can I do this? I have tried to register an Infura account and use it to interact with the function, the python code runs smoothly, but I can't see any changes to the smart contract. So I'm wondering how I can realize this goal. Thanks in advance.

My code logic is as follows.

w3 = Web3(Web3.HTTPProvider('https://kovan.infura.io/v3/...(my address)'))
ctr = w3.eth.contract(address=address, abi=abi) # address and abi are both specified previously
ctr.functions.my_func(input).call()

Best Answer

Any smart contract call cannot change the Ethereum state.

You need to perform a transaction and pay the gas fee to make any state changes. There are no free state changes.

Use transact() instead of call(). You will also need to set up a local private key.

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You can use web3py.

And if you need to compile contracts - use solc.

Web3.py – How to Call a Smart Contract Function in Python Script

Here is an example using Brownie that should help:

import time
from brownie import Contract, network, web3


abi = {}          # contract ABI as a dict
address = "0x00"  # contract address as a string


network.connect('mainnet')
my_contract = Contract("MyContractName", address, abi=abi)

height = web3.eth.blockNumber

while True:
    result = my_contract.myCallableFn(arg1, arg2) # change to call the desired method
    if result == desired_result:
        # do whatever you need to do

    while web3.eth.blockNumber == height:
        time.sleep(1)
    height = web3.eth.blockNumber

You will have to modify some configuration settings to point at your own node, or set an infura API key in your environment variables.

The documentation on accessing contract methods might also be useful if my example is unclear.

Hope this helps.

Best Answer

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Web3.py – How to Call a Smart Contract Function in Python Script

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