gh-104050: Argument clinic: improve typing around adding C converters #107209
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| CConverterClassT = TypeVar("CConverterClassT", bound=type["CConverter"]) | ||
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| def add_c_converter( | ||
| f: type[CConverter], | ||
| f: CConverterClassT, | ||
| name: str | None = None | ||
| ) -> type[CConverter]: | ||
| ) -> CConverterClassT: |
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By using a TypeVar here (and with the other functions in this PR), we can make the annotation much more expressive.
The annotation currently says "you put in an object f that's some subtype of type[CConverter], and you get out an object that's some subtype of type[CConverter].
The new annotation, by contrast, says, "you put in an object f, and you get out an object that has the same type as whatever the type of f is, as long as the type of f is a subtype of type[CConverter].
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As an example, with the following snippet:
x = add_c_converter(bool_converter)Mypy would have inferred the type of x to be type[CConverter] with the current annotation. But with the new annotation, mypy should be able to infer that the type of x is bool_converter.
Some of this looks a little complicated at first glance, but it's hopefully not too hard to grok