Support factory= in attr plugin. #5005
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It works pretty much like default=
| attr_has_factory = bool(_get_argument(rvalue, 'factory')) | ||
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| if attr_has_default and attr_has_factory: | ||
| ctx.api.fail("Can't pass both `default` and `factory`.", rvalue) |
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It is a good idea to always add tests for any newly added error messages.
| @attr.s | ||
| class A: | ||
| x: List[int] = attr.ib(factory=list) | ||
| y: int = attr.ib(factory=my_factory) |
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Please add also a test where this fails due to a wrong return type of the factory function.
mypy/plugins/attrs.py
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| if attr_has_default and attr_has_factory: | ||
| ctx.api.fail("Can't pass both `default` and `factory`.", rvalue) | ||
| elif attr_has_factory: | ||
| attr_has_default = attr_has_factory |
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I think attr_has_default = True would be shorter and cleaner.
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Done and done! |
test-data/unit/lib-stub/attr.pyi
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| factory: Optional[Callable[[], _T]] = ..., | ||
| ) -> _T: ... | ||
| # This form catches explicit None or no default but with no other arguments returns Any. | ||
| # This form catches explicit None or no default but with no other arguments returns Any. |
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This line is repeated twice.
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| _T = TypeVar('_T') | ||
| _C = TypeVar('_C', bound=type) | ||
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| _ValidatorType = Callable[[Any, Any, _T], Any] |
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I thought validator should return bool, isn't this the case?
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The return value of validators is ignored. A validation error is a raised exception. However I don't want to force a "None"
test-data/unit/check-attr.test
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| import attr | ||
| @attr.s | ||
| class A: | ||
| x: int = attr.ib(factory=list) # E: Incompatible types in assignment (expression has type "List[T]", variable has type "int") |
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The error message looks a bit cryptic. Why it is List[T] and not List[Any]? There is no T in code. I suppose this might be a bug in using class as factory, is the error better if you use a generic function instead of class?
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This error come from the stubs not from the plugin (i.e. any method that takes a type would give this error message.) I can add a generic function too.
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Thanks for the quick review. Your requests have been implemented. |
This is a new feature in attrs 18.1
The implementation is just like
default=