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I am using solidity 0.7.4, web3.py 5.12.2, and python 3.7.

I am working with Windows 10.

My goal is to emit an event inside a solidity function, in order to retrieve the log after the function is executed.

This is my event event logString(string arg);

And this is how I emit the event emit logString("example string");

On Remix it works, and I am able to retrieve the string I emit, in the log of the transaction.

When I try it on Python, it doesn't work.

This is my Python code:

web3_instance = Web3(HTTPProvider("http://"+host+":"+port, request_kwargs={'timeout': timeout}))
Platform_contract= web3_instance.eth.contract(address=contract_address, abi=abi, bytecode=bytecode)
coinbase= web3_instance.eth.coinbase
functions= Platform_contract.functions

tx_hash =functions.market_clearing(n_clearings, 
t_clearing_first,supplier_bids,uniform_pricing,discriminative_pricing).transact({'from': coinbase})
tx_receipt = web3_instance.eth.getTransactionReceipt(tx_hash)

log_to_process = tx_receipt['logs'][0]
processed_log = Platform_contract.events.logString().processLog(log_to_process)
log = processed_log['args']['arg']

Unfortunately tx_receipt['logs'] is empty and I get an exception.

Do you know how can I retrieve the log of the event?

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  • Did you wait the transaction to me be mined? – Mikko Ohtamaa Nov 19 '20 at 19:17
  • Of course. I even stopped the execution with the debugger. I can clearly see the transaction hash on ganache-cli and I am able to retrieve the transaction receipt. Just the logs are empty. It works on the remix debugger though. – Marcello Feroce Nov 19 '20 at 19:40
  • It seems like when I deploy (migrate ) from Truffle, the logs of the transactions are empty. I don't know why – Marcello Feroce Nov 20 '20 at 8:46
  • Also see that you are using the web3.py API correctly - there is specifically a method of getting past events – Mikko Ohtamaa Nov 20 '20 at 9:31
  • Can you please help me to find it? The documentation is poor. And actually my code works when the contract is deployed by remix. – Marcello Feroce Nov 20 '20 at 13:21
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I managed to solve the problem. I don't know why, I had to exactly specify the network_id in the truffle config.js. Then I migrated the contracts again and ran ganache-cli on that specific network_id.

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