[Ethereum] How to get event logs in web3.py v3.*

web3.py

I would like to listen to events on a contract, but I'm having trouble figuring out which of the interfaces is the correct one and finding an example on how to use it.

The way I see it:

Contract.eventFilter is v4 only
Contract.pastEvents is v3 only
LogFilter is v3 only and marked as deprecated, pointing to:
LogFilter.get_all_entries – v4 only
LogFilter.get is only in v3
and there are many many more…

The most promising is combination of Eth.filter with either:

Eth.getFilterChanges for listening to new events or
Eth.getFilterLogs for fetching them from history.

Which method should I use so that it will keep working once v4 comes out?

Best Answer

You've got it. The best way to be compatible with both is to use either of:

w3.eth.getFilterChanges()
w3.eth.getFilterLogs()

The good news is that the work is reusable. You'll probably want some kind of polling thread to get the filter changes in v3, and a similar thread will be useful in a port to v4.

The bad news is that it's one of the least convenient ways to write filters. I would suggest to go straight to v4 now, but filters in particular need a lot of love in the beta. Block and transaction filters are simply broken at the moment: https://github.com/ethereum/web3.py/pull/490

If you're feeling really motivated, you could cherry-pick the changes from this PR back to the v3 branch. Then you could write the v4-compatible filter code in v3.

Related Solutions

[Ethereum] How to get transaction details from filter in web3.py

The docs you linked to are showing examples from filtering for events. Since you are filtering for pending transactions, it will be a bit different.

When listing pending transactions, you only get the transaction hashes, as specified in the json-rpc spec:

For filters created with eth_newPendingTransactionFilter the return are transaction hashes (DATA, 32 Bytes), e.g. ["0x6345343454645..."].

So you would get the list of transaction details using something like:

transaction_hashes = web3.eth.getFilterChanges(web3_filter.filter_id)
transactions = [web3.eth.getTransaction(h) for h in transaction_hashes]

[Ethereum] web3.py event listener functionality doesn’t catch events

had the same issue and reproted it. See here the discussion. No solution yet.

However, the old method works fine, for instance:

myfilter = mycontract.eventFilter('EventName', {'fromBlock': 0,'toBlock': 'latest'});
eventlist = myfilter.get_all_entries()

This will work.

hope this helps

Best Answer

Related Solutions

[Ethereum] How to get transaction details from filter in web3.py

[Ethereum] web3.py event listener functionality doesn’t catch events

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