Fix TypeError in ContractFunction.call when args and kwargs properties are None

[iwiwi]

Fix #2541.

I confirmed that the example code in #2541 passes with this change.

If you want me to add related tests in the same PR, as I am new to this project, I would appreciate if you could give some hints, e.g., similar existing tests, where to put tests (a new file or existing file?), etc.

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My cats 😺

[kclowes]

Your cats are very cute!

We will need to add a test before merging. I don't really see an obvious home for where the test, but I think if you model it after the tests in tests/core/contracts/test_ambiguous_functions.py but put the test in tests/core/contracts/test_contract_call_interface.py that would be best. I haven't looked too closely, but it looks like there is a test that is similar to what you are running into, but the test is passing here. Can you tell why that test is passing but you're running into the TypeError? Thanks!

[iwiwi]

Thanks for useful pointers!

web3.py/tests/core/contracts/test_contract_ambiguous_functions.py

Lines 179 to 183 in 2bf7e9e

	def test_contract_function_methods(string_contract):
	set_value_func = string_contract.get_function_by_signature('setValue(string)')
	get_value_func = string_contract.get_function_by_signature('getValue()')
	assert isinstance(set_value_func('Hello').transact(), HexBytes)
	assert get_value_func().call() == 'Hello'

The difference between my snippet and this test is that, in this test, ContractFunction.__call__ is called before calling ContractFunction.call. That is, if we change L183 from assert get_value_func().call() == 'Hello' to assert get_value_func.call() == 'Hello', it will cause the same type errors.

What do you think?

• My opinion is that, even before calling ContractFunction.__call__, as it is indeed a ContractFunction instance, I think it should be callable. So I think we should apply my fix.
• Another option is to consider this as a design. That is, we distinguish two kinds of ContractFunction: (1) instances before invoking __call__ (which we cannot call), and (2) instances after invoking __call__ (which we can call). We may improve error messages and documents.