Upgrade to latest mypy

[achidlow]

PEP-484 has changed to recommend against implicit optionals based on default arguments, and mypy has accordingly flipped the default in a recent release.

ref: https://peps.python.org/pep-0484/#union-types

[CLAassistant]

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[barnjamin]

@tzaffi I recall seeing a recent commit from you switching the thing | None type hint to Optional[thing], was there a specific reason for that?

[tzaffi]

@tzaffi I recall seeing a recent commit from you switching the thing | None type hint to Optional[thing], was there a specific reason for that?

These are semantically equivalent. I think we ought to come to an agreement about what style we ought to adopt going forward -so we don't need to spend any mental calories on it. I propose:

• use Optional[TheType] instead of TheType | None
• Use TheFirstType | TheSecondType instead of Union[TheFirstType, TheSecondType]

Why? I don't really have a good reason. I could be easily swayed to another viewpoint. But we should adopt some style.

[tzaffi]

👍

[barnjamin]

@achidlow noted that the use of Union/Optional are required if the type must be quoted

[tzaffi]

@achidlow noted that the use of Union/Optional are required if the type must be quoted

That's an argument for not using | at all.

[tzaffi]

Thanks for upgrading mypy!

I had a small nit regarding the Makefile.

Also, I won't hold up the PR on account of this, but I created #619 and suggested that we disallow | for annotations going forward.

[achidlow]

@tzaffi pending the outcome of #619, I've at least made this PR internally consistent in the use of | over Optional. If you'd prefer it the other way around for now I'm happy to flip that for all the methods changed in this PR.

[tzaffi]

Why drop the --show-error-codes arg? It's been handy on occasion.

[achidlow]

Not sure if this used to be flipped in a previous mypy version, but that's the default and assumed. You have to disable it with --hide-error-codes

[tzaffi]

Thanks for explaining. Yeah, it got flipped: https://github.com/python/mypy/blob/release-0.940/docs/source/error_codes.rst#displaying-error-codes

[tzaffi]

Looks great, thank you!