Uses Self Type in contract factory methods

[konichuvak]

What was wrong?

1. Return type of Contract.factory() is erroneously annotated as "Contract" instead of Type["Contract"]

2. Even once we fix the error above, type annotation for subclasses of Contract are broken

from typing import Type

from web3 import Web3
from web3.contract import Contract


class MyContract(Contract):
    address = Web3.to_checksum_address("0x0000000000000000000000000000000000000000")

    @classmethod
    def factory(cls, *args, **kwargs) -> Type["Contract"]:
        return super().factory(*args, **kwargs)

    def my_method(self):
        pass

contract_factory = MyContract.factory(Web3())()
contract_factory.my_method()  # error: "Contract" has no attribute "my_method"  [attr-defined]

How was it fixed?

Self Type was added in Python 3.11 which solves this problem of underspecified return types of constructor methods for subclasses.

Todo:

• Add entry to the release notes

Cute Animal Picture

[pacrob]

Self is definitely a helpful addition, but we need to maintain compatibility with all active versions of python. 3.7 is being deprecated soon, but it'll be a while before we can use features that are brand new in 3.11.

I'll leave this open in case you want to try a different solution that maintains compatibility.

[konichuvak]

Self is definitely a helpful addition, but we need to maintain compatibility with all active versions of python. 3.7 is being deprecated soon, but it'll be a while before we can use features that are brand new in 3.11.

I'll leave this open in case you want to try a different solution that maintains compatibility.

Thanks for reviewing the PR.
I am not sure which part is incompatible with Python3.7 in here? We are importing Self from typing_extensions, which supports 3.7 and above.

[pacrob]

OK, dug in a bit further. You are correct that we can use Self with earlier python versions, which is great news. It looks like mypy doesn't support it until v1.0.0 though, and when I bump that it opens a number of other typing issues to deal with.

Once we get that in, I'll come back and pull this in. Thank you!

[konichuvak]

It looks like mypy doesn't support it until v1.0.0 though

Great point, I did not catch that.
I bumped it to >=1.0.0 and fixed / ignored all the typing issues that popped up as a result!
For the exception of the ones in ethpm-spec which I am not sure how to deal with. It seems like that module is only type-checked when when mypy is ran locally.

[pacrob]

ethpm is being deprecated, so probably OK to drop it from mypy checking. I'm not sure why the CI insists on running on your account though - it usually switches to our resources once I push a commit. Maybe try deleting the web3.py project from your CircleCI account?

I've branched it in #3001 and CI is passing there, so we can just use that if we can't get it to run here.

[pacrob]

Thanks for this, @konichuvak ! Your original commits are merged in #3001