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gh-104050: Argument clinic: improve typing around adding C converters #107209

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Jul 25, 2023
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gh-104050: Argument clinic: improve typing around adding C converters #107209

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20 changes: 13 additions & 7 deletions Tools/clinic/clinic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@
NoReturn,
Protocol,
TypeGuard,
TypeVar,
overload,
)

Expand Down Expand Up @@ -2647,10 +2648,12 @@ def __getattribute__(self, name: str) -> Any:
fail("Stepped on a land mine, trying to access attribute " + repr(name) + ":\n" + self.__message__)


CConverterClassT = TypeVar("CConverterClassT", bound=type["CConverter"])

def add_c_converter(
f: type[CConverter],
f: CConverterClassT,
name: str | None = None
) -> type[CConverter]:
) -> CConverterClassT:
Comment on lines +2651 to +2656
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@AlexWaygood AlexWaygood Jul 24, 2023 •
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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.

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Neat!

if not name:
name = f.__name__
if not name.endswith('_converter'):
Expand All @@ -2659,7 +2662,7 @@ def add_c_converter(
converters[name] = f
return f

def add_default_legacy_c_converter(cls):
def add_default_legacy_c_converter(cls: CConverterClassT) -> CConverterClassT:
# automatically add converter for default format unit
# (but without stomping on the existing one if it's already
# set, in case you subclass)
Expand All @@ -2670,16 +2673,19 @@ def add_default_legacy_c_converter(cls):

def add_legacy_c_converter(
format_unit: str,
**kwargs
) -> Callable[[ConverterType], ConverterType]:
**kwargs: Any
) -> Callable[[CConverterClassT], CConverterClassT]:
"""
Adds a legacy converter.
"""
def closure(f):
def closure(f: CConverterClassT) -> CConverterClassT:
added_f: Callable[..., CConverter]
if not kwargs:
added_f = f
else:
added_f = functools.partial(f, **kwargs)
# mypy's special-casing for functools.partial
# can't quite grapple with this code here
added_f = functools.partial(f, **kwargs) # type: ignore[arg-type]
if format_unit:
legacy_converters[format_unit] = added_f
return f
Expand Down