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GH1226 Add Styler.map to the stubs #1228

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Merged
merged 7 commits into from
May 23, 2025
Merged

GH1226 Add Styler.map to the stubs #1228

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7a47b42
GH1226 Add Styler.map to the stubs
loicdiridollou May 21, 2025
a3357a3
Update pandas-stubs/io/formats/style.pyi
loicdiridollou May 21, 2025
85eac7a
GH1226 PR Feedback
loicdiridollou May 21, 2025
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GH1226 PR Feedback
loicdiridollou May 21, 2025
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GH1226 PR Feedback
loicdiridollou May 21, 2025
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GH1226 PR Feedback
loicdiridollou May 23, 2025
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GH1226 PR Feedback
loicdiridollou May 23, 2025
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13 changes: 13 additions & 0 deletions pandas-stubs/io/formats/style.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -71,6 +71,19 @@ class Styler(StylerRenderer):
formatter: ExtFormatter | None = ...,
) -> None: ...
def concat(self, other: Styler) -> Styler: ...
@overload
def map(
self,
func: Callable[[Scalar], str | None],
subset: Subset | None = ...,
) -> Styler: ...
@overload
def map(
self,
func: Callable[..., str | None],
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@Dr-Irv I could not find how to type a function that takes Scalar and some other stuff, I tried [Scalar, ...] but it was not happy, feel free to recommend something better.

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Callable cannot express complex signatures

I think this is usually done using Protocol, I tried writing this:

    class _MapCallable(Protocol):
        def __call__(self, first_arg: Scalar, /, *args: Any, **kwargs: Any) -> str | None: ...

    def map(
        self,
        func: _MapCallable,
        subset: Subset | None = ...,
        **kwargs: Any,
    ) -> Styler: ...

but it fails the test

tests/test_styler.py:256: error: Expression is of type "Any", not "Styler"  [assert-type]
tests/test_styler.py:257: error: No overload variant of "map" of "Styler" matches argument types "Callable[[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any], str], str | None]", "str"  [call-overload]
tests/test_styler.py:257: note: Possible overload variants:
tests/test_styler.py:257: note:     def map(self, func: Callable[[str | bytes | date | datetime | timedelta | <7 more items> | complex | integer[Any] | floating[Any] | complexfloating[Any, Any]], str | None], subset: _IndexSlice | slice[Any, Any, Any] | tuple[slice[Any, Any, Any], ...] | list[Any] | Index[Any] | None = ...) -> Styler
tests/test_styler.py:257: note:     def map(self, func: _MapCallable, subset: _IndexSlice | slice[Any, Any, Any] | tuple[slice[Any, Any, Any], ...] | list[Any] | Index[Any] | None = ..., **kwargs: Any) -> Styler

Maybe this will be helpful to figure something out.

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The idea of using the Protocol works if we change the test. Instead of

    def color_negative(v: Scalar,  color: str) -> str | None:

if we use

    def color_negative(v: Scalar,  /, color: str) -> str | None:

then it is fine. Note that pyright accepts the func without the / defined, but mypy doesn't, so this is a workaround to make mypy happy.

@loicdiridollou change the test that way and put the _MapCallable near the other Protocol definition in that file and we should be good to go.

@Molkree Thanks for the suggestion!

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Note that pyright accepts the func without the / defined, but mypy doesn't, so this is a workaround to make mypy happy.

I had to double check that and I agree that this is mypy bug. According to these typing rules callable with standard argument of matching type should be assignable to the positional-only argument of matching type, same for kwargs but because we typed them as Any everything should be assignable to everything.

I think it's this bug specifically: python/mypy#12525 (or a variation of it, error messages are not the same)

You learn something new everyday!

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Thanks for all the feedback here, indeed I learn about those intricacies and mypy issues!
My only fear is that it would force people to have the argument-based function with the /, but I think it is worth trying out and seeing if we get complaints from the user base.

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Thanks for all the feedback here, indeed I learn about those intricacies and mypy issues! My only fear is that it would force people to have the argument-based function with the /, but I think it is worth trying out and seeing if we get complaints from the user base.

It only forces people who use mypy to include /. If you use pyright, it isn't required.

subset: Subset | None = ...,
**kwargs: Any,
) -> Styler: ...
def set_tooltips(
self,
ttips: DataFrame,
Expand Down
28 changes: 27 additions & 1 deletion tests/test_styler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,6 @@

DF = DataFrame({"a": [1, 2, 3], "b": [3.14, 2.72, 1.61]})


PWD = pathlib.Path(os.path.split(os.path.abspath(__file__))[0])

if TYPE_CHECKING:
Expand Down Expand Up @@ -233,3 +232,30 @@ def test_styler_columns_and_index() -> None:
styler = DF.style
check(assert_type(styler.columns, Index), Index)
check(assert_type(styler.index, Index), Index)


def test_styler_map() -> None:
"""Test type returned with Styler.map GH1226."""
df = DataFrame(data={"col1": [1, -2], "col2": [-3, 4]})
check(
assert_type(
df.style.map(
lambda v: "color: red;" if isinstance(v, float) and v < 0 else None
),
Styler,
),
Styler,
)

def color_negative(v: Scalar, color: str) -> str | None:
return f"color: {color};" if isinstance(v, float) and v < 0 else None

df = DataFrame(np.random.randn(5, 2), columns=["A", "B"])

check(
assert_type(
df.style.map(color_negative, color="red"),
Styler,
),
Styler,
)