Support overloaded events when finding event ABI

[Pet3ris]

What was wrong?

Related to Issue #1704.

How was it fixed?

Make sure event arguments are used to disambiguate events (in addition to names) when overloaded events are present.

Todo:

• Add entry to the release notes

Cute Animal Picture

[wolovim]

Thanks for the PR! If we don't have a test that includes overloaded events, we ought to include one. If you're up for taking that on, great, otherwise I can take over.

[Pet3ris]

@marcgarreau please do - this was a very incremental change without broader context!

[Pet3ris]

I don't think I fully solved the underlying root cause. One observation:

• For an event that's generated from factory (part of <web3_contract>.events) <event>.abi can sometimes be None and calling <event>.get_event_abi() directly cannot be used as a work-around as there is now way to pass in the arguments

[wolovim]

Yeah, there's a bit more to the story here. In doing some quick tests, looks like the effects can be seen through more APIs. For example, contract_instance.events.OverloadedEvent.getLogs() returns a ValueError: Multiple events found. Will dig in deeper tomorrow.

edit: I guess there's an argument to be made here that that's a desirable response instead of lumping both event's logs together, for example. This events API isn't exactly friendly to overloading.

[pipermerriam]

A brief scan of our code that handles contract events suggests we have no handling in place for multiple events with the same name.

one example here:

web3.py/web3/contract.py

Lines 231 to 244 in b9d7677

	def __init__(self, abi: ABI, web3: 'Web3', address: Optional[ChecksumAddress] = None) -> None:
	if abi:
	self.abi = abi
	self._events = filter_by_type('event', self.abi)
	for event in self._events:
	setattr(
	self,
	event['name'],
	ContractEvent.factory(
	event['name'],
	web3=web3,
	contract_abi=self.abi,
	address=address,
	event_name=event['name']))

It will take a bit of clever problem solving to improve these APIs to support this, but it should be largely doable.

1. If we have two similarly named events we should probably expose a mechanism that would allow direct access by topic if the topic is known.
2. If the user is creating a filter, and the filter contains any filters against the arguments (indexed or not) we typically be capable of determining which of the duplicate named events the filter is intended for by matching against argument types.
3. In the case that there are duplicate named events and we cannot determine which event is intended which is definitely going to be an unavoidable case, we need to be clever and construct the filter such that it matches all of the event topics for the various overloaded events.

We already do similar things for functions, but there we have the luxury of always having the arguments and thus only rarely can we not differentiate between functions with duplicate names. But I think with events we have the advantage of not actually ending up in a situation where we cannot do what the user wants, it just might end up containing extra logs that they don't want since we'll over-match on the filter parameters since we'll have to provide multiple topics.

[Pet3ris]

FWIW, my specific need (that this PR doesn't solve yet) was to get access to an overloaded event's ABI. Seems like neither <event>.abi nor <event>._get_event_abi() works at this stage but I'm not 100% this is an intended part of the web3.py API. As you both indicate, there are lots of other positive implications related to fixing overloaded events.

[ptrcarta]

Is there a suggested workaround? I'm incurring in this when trying to query the ActionPaused events of Compound Comptroller, which is overloaded

[dthinkr]

Here is a further fix of the issue. Change find_matching_event_abi to avoid it from throwing an error. Instead, let it return the first element.

if len(event_abi_candidates) >= 1: return event_abi_candidates[0]
After the fix, I was able to run this with no problem.

events = contract.events.File(*argument_names).getLogs(fromBlock=start_block, toBlock=end_block)