Teach mypy plugin that validator methods are classmethods #4102
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For your consideration: a patch which implements the suggestion I made here: pydantic#4101 Briefly: pydantic automatically wraps validator methods using `@classmethod`. Hence the first argument to a user-provided validator should be `cls`. But mypy doesn't know this: it analyses validator methods like any other regular method, believing the first parameter `cls` to be a model instance (usually denoted self). This means that if one annotates `cls` as `Type[...]` then mypy believes raises an error: error: The erased type of self "Type[temp.Model]" is not a supertype of its class "temp.Model" I concede that this is an extremely niche thing. The only tangible end-user benefit I can think of is that it'll stop you from calling instance methods in a validator. ---- I haven't written a mypy plugin before, so this is a bit of a hack-until-it-works. But it was more straightforward than I expected to get something working!
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please review |
samuelcolvin
reviewed
Aug 8, 2022
tests/mypy/modules/plugin_success.py
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| name: str | ||
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| @validator('name') | ||
| def noop_validator_with_annotations(cls: Type['ModelWithAnnotatedValidator'], name: str) -> str: |
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I think this is wrong, surely (like self) you can omit the type hint for cls?
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Ahh yes. I think I'd put this in so that the test failed without the change. Let me see if I can come up with something better.
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otherwise LGTM. Please update. Also conflicts. |
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Many thanks for reviewing. I've merged in master and updated the tests. Please review. |
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assigned hramezani, PrettyWood and samuelcolvin and unassigned DMRobertson
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thanks so much. |
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For your consideration: a patch which implements the suggestion I made here:
#4101
Briefly: pydantic automatically wraps validator methods using
@classmethod. Hence the first argument to a user-provided validatorshould be
cls. But mypy doesn't know this: it analyses validatormethods like any other regular method, believing the first parameter
clsto be a model instance (usually denoted self).This means that if one annotates
clsasType[...]then mypybelieves raises an error:
I concede that this is an extremely niche thing. The only tangible
end-user benefit I can think of is that it'll stop you from calling
instance methods in a validator.
I haven't written a mypy plugin before, so this is a bit of a
hack-until-it-works. But it was more straightforward than I expected to
get something working!
Change Summary
Related issue number
fix #4101
Checklist
changes/<pull request or issue id>-<github username>.mdfile added describing change(see changes/README.md for details)