Make Instance type hints more useful #1840
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mdickinson
commented
Mar 5, 2025
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| class Fruit: | ||
| info = Str("good for you") | ||
| info: str |
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Drive-by change: it looks as though Fruit was trying to pretend to be a HasTraits class but without actually inheriting from HasTraits, so the __init__ implementation didn't make a lot of sense. I've changed it to be a plain old Python class.
mdickinson
commented
Mar 5, 2025
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| class Instance(BaseInstance[_S]): | ||
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| @overload |
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I couldn't find a way not to have to repeat these overloads - simply doing class Instance(BaseInstance): ... led to anything being accepted for the trait values. Hints welcome.
mdickinson
commented
Mar 5, 2025
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Pinging @siddhantwahal for interest. |
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Note: #1838 should be merged first - we can't trust the type hint tests until it is.Done.Closes #1839
Closes #1764
Closes #1673
This PR provides a better type-hinting experience for
Instance(andBaseInstance) traits:strin the inferred type for the value of anInstancetraitallow_none=False, so that type checkers can infer that the value of the trait is notNone(andNonemay not be assigned) in this case. Note: this technically isn't true (since a default ofNonecan still be provided even whenallow_none=False), but it's a safe bet that if the user is explicitly statingallow_none=Falsethen the intent is that the trait value is neverFalseAnyfor the value trait (for both getting and setting).