web3.eth.contract with no abi

[deandunbar]

• Version: 5.29.1
• Python: 3.10.4
• OS: linux
• pip freeze output

eth-abi==2.1.1
eth-account==0.5.7
eth-hash==0.3.2
eth-keyfile==0.5.1
eth-keys==0.3.4
eth-rlp==0.2.1
eth-typing==2.3.0
eth-utils==1.10.0
web3==5.29.1

What was wrong?

testContract = w3.eth.contract(address=add)
testContract.get_function_by_selector("0x370158ea")
Gives an error:

  File "/home/dean/.local/lib/python3.10/site-packages/web3/_utils/abi.py", line 89, in filter_by_type
    return [abi for abi in contract_abi if abi['type'] == _type]
TypeError: 'NoneType' object is not iterable

running the same commands but with abi included gives the correct value:
testContract = web3.eth.contract(address=add,abi=abi)
testContract.get_function_by_selector("0x370158ea")
<Function info()>

The documentation documentation
Does not show abi as a required parameter when instantiating the Contract class. But all the examples show it being used.
I can instantiate a contract by passing it an address without an abi parameter. But later calls fail. Is this expected behavior?
I should still be able to interact with the bytecode at a specific address as long as I can either generate a function signature or call the selector directly.

Is it expected behavior to require abi for all contract interaction, even those that don't require it?

Please include any of the following that are applicable:

• The code which produced the error
• The full output of the error
• What type of node you were connecting to.

I used a remote infura node. I noticed this issue when working with brownie and verified that it was happening in using web3 directly.

How can it be fixed?

Updating the documentation if this is expected behavior. If this is not expected behavior then adding a check on for set abi on the contract function calls.

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[deandunbar]

I want to make sure I reiterate that I know in most common usage of web3.py you would need to have the abi.
I am working on some security tooling to interact with contracts without abi by generating the signature for the function call based on name and input params/expected output type or having the selector.

[kclowes]

I believe if you are interacting through a contract instance, the ABI is required. A check and/or documentation could certainly be improved, so I'll leave this open. If you want to work around that, you can just use w3.eth.build_transaction/w3.eth.call/w3.eth.send_transaction etc. What's your use case for interacting with a contract object without the ABI?

[deandunbar]

Thank you, yes if this is expected behavior I can see about adding to the documentation.

I am working on offensive security tooling for interacting with contracts. The abi is not always available and being able to call the function signature directly helps in certain reversing flows.
To be fair, it sounds like I am working on an edge case and there might not be any merit in merging any of the lower level calls to web3.py.
I can directly call the loaded address and encode the function selector manually via abi.endodeWithSingature("foo(uint256)", "call foo", 123)

I can look at the code, but if the web3.py library is calling the same function under the hood then there is no technical requirement for needing the abi when calling by function selector. If that is the case, is there any reason for enforcing the need of abi for those lower level calls?

[kclowes]

Yeah, we do not call abi.encodeWithSignature under the hood. And following the function calls, the ABI does get used a lot, so documenting that the ABI is required is probably the best path for now. Thanks!