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BUG: allow kwargs in Styler apply_index and map_index #1725

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BUG: allow kwargs in Styler apply_index and map_index #1725

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12 changes: 10 additions & 2 deletions pandas-stubs/io/formats/style.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,11 @@ class _SeriesFunc(Protocol):
self, series: Series, /, *args: Any, **kwargs: Any
) -> list[Any] | Series: ...

class _SeriesStrFunc(Protocol):
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@loicdiridollou loicdiridollou Apr 15, 2026

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I tried on my end and this protocol thing works but is a bit of overkill for what you are trying to do here. Turns out since args and kwargs here are just Any, you can drop it in exchange for:
Callable[Concatenate[Series, ...]], list[str] | np_ndarray_str | Series[str]]
This will make it a lot cleaner and simpler to understand.

def __call__(
self, series: Series[str], /, *args: Any, **kwargs: Any
) -> list[str] | Series[str]: ...

class _DataFrameFunc(Protocol):
def __call__(
self, series: DataFrame, /, *args: Any, **kwargs: Any
Expand Down Expand Up @@ -277,14 +282,17 @@ class Styler(StylerRenderer):
) -> Styler: ...
def apply_index(
self,
func: Callable[[Series], list[str] | np_ndarray_str | Series[str]],
func: (
_SeriesStrFunc
| Callable[[Series], list[str] | np_ndarray_str | Series[str]]
),
axis: Axis = ...,
level: Level | list[Level] | None = ...,
**kwargs: Any,
) -> Styler: ...
def map_index(
self,
func: Callable[[Scalar], str | None],
func: _MapCallable | Callable[[Scalar], str | None],
axis: Axis = ...,
level: Level | list[Level] | None = ...,
**kwargs: Any,
Expand Down
13 changes: 13 additions & 0 deletions tests/test_styler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -76,13 +76,26 @@ def f1(s: Series) -> Series[str]:

check(assert_type(DF.style.apply_index(f1), Styler), Styler)

# GH 1723
def highlight_odd(index: pd.Series, /, color: str) -> list[str]:
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@loicdiridollou loicdiridollou Apr 15, 2026

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No need for the /, it should work without it since it is hardly a usecase you see in production code.

return [f"color: {color}" if x % 2 else "" for x in index]

check(
assert_type(DF.style.apply_index(highlight_odd, color="purple"), Styler), Styler
)


def test_map_index() -> None:
def f(s: Scalar) -> str | None:
return "background-color: yellow;" if s == "B" else None

check(assert_type(DF.style.map_index(f), Styler), Styler)

def f1(s: Scalar, /, color: str) -> str | None:
return f"background-color: {color};" if s == "b" else None

check(assert_type(DF.style.map_index(f1, color="pink"), Styler), Styler)


def test_background_gradient() -> None:
check(assert_type(DF.style.background_gradient(), Styler), Styler)
Expand Down