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GeezerVison is showing github.com — gh-104050: Argument clinic: improve typing around adding C converters by AlexWaygood · Pull Request #107209 · python/cpython

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@AlexWaygood

@AlexWaygood AlexWaygood commented Jul 24, 2023 •
edited by bedevere-bot
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Some of this looks a little complicated at first glance, but it's hopefully not too hard to grok

  • Issue: Add type annotations to clinic.py #104050

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@AlexWaygood
Argument clinic: improve typing around adding C converters
046ab5a
@AlexWaygood AlexWaygood added the skip news label Jul 24, 2023
@AlexWaygood
AlexWaygood requested a review from erlend-aasland as a code owner July 24, 2023 22:41
@bedevere-bot bedevere-bot added the awaiting core review label Jul 24, 2023
@bedevere-bot bedevere-bot mentioned this pull request Jul 24, 2023
Add type annotations to clinic.py #104050
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AlexWaygood
AlexWaygood commented Jul 24, 2023
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Comment thread Tools/clinic/clinic.py
Comment on lines +2651 to +2656
CConverterClassT = TypeVar("CConverterClassT", bound=type["CConverter"])

def add_c_converter(
f: type[CConverter],
f: CConverterClassT,
name: str | None = None
) -> type[CConverter]:
) -> CConverterClassT:

@AlexWaygood AlexWaygood Jul 24, 2023 •
edited
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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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@AlexWaygood AlexWaygood Jul 24, 2023

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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.

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@erlend-aasland erlend-aasland Jul 25, 2023

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Neat!

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erlend-aasland
erlend-aasland approved these changes Jul 25, 2023
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Thanks!

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@bedevere-bot bedevere-bot added awaiting merge and removed awaiting core review labels Jul 25, 2023
@AlexWaygood
AlexWaygood merged commit dbfe738 into python:main Jul 25, 2023
@bedevere-bot bedevere-bot removed the awaiting merge label Jul 25, 2023
@AlexWaygood
AlexWaygood deleted the add-converter-typing branch July 25, 2023 08:18
jtcave pushed a commit to jtcave/cpython that referenced this pull request Jul 27, 2023
@AlexWaygood @jtcave
pythongh-104050: Argument clinic: improve typing around adding C conv…
2675e87 
…erters (python#107209)
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@erlend-aasland erlend-aasland erlend-aasland approved these changes

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@AlexWaygood @erlend-aasland @bedevere-bot
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