Method apply

pandas/io/formats/style.py:1984–2073

Apply a CSS-styling function column-wise, row-wise, or table-wise. Updates the HTML representation with the result. Parameters ---------- func : function ``func`` should take a Series if ``axis`` in [0,1] and return a list-like objec

(
        self,
        func: Callable,
        axis: Axis | None = 0,
        subset: Subset | None = None,
        **kwargs,
    )

        return self

    def apply(
        self,
        func: Callable,
        axis: Axis | None = 0,
        subset: Subset | None = None,
        **kwargs,
    ) -> Styler:
        """
        Apply a CSS-styling function column-wise, row-wise, or table-wise.

        Updates the HTML representation with the result.

        Parameters
        ----------
        func : function
            ``func`` should take a Series if ``axis`` in [0,1] and return a list-like
            object of same length, or a Series, not necessarily of same length, with
            valid index labels considering ``subset``.
            ``func`` should take a DataFrame if ``axis`` is ``None`` and return either
            an ndarray with the same shape or a DataFrame, not necessarily of the same
            shape, with valid index and columns labels considering ``subset``.
        axis : {0 or 'index', 1 or 'columns', None}, default 0
            Apply to each column (``axis=0`` or ``'index'``), to each row
            (``axis=1`` or ``'columns'``), or to the entire DataFrame at once
            with ``axis=None``.
        subset : label, array-like, IndexSlice, optional
            A valid 2d input to `DataFrame.loc[<subset>]`, or, in the case of a 1d input
            or single key, to `DataFrame.loc[:, <subset>]` where the columns are
            prioritised, to limit ``data`` to *before* applying the function.
        **kwargs : dict
            Pass along to ``func``.

        Returns
        -------
        Styler
            Instance of class with CSS applied to its HTML representation.

        See Also
        --------
        Styler.map_index: Apply a CSS-styling function to headers elementwise.
        Styler.apply_index: Apply a CSS-styling function to headers level-wise.
        Styler.map: Apply a CSS-styling function elementwise.

        Notes
        -----
        The elements of the output of ``func`` should be CSS styles as strings, in the
        format 'attribute: value; attribute2: value2; ...' or,
        if nothing is to be applied to that element, an empty string or ``None``.

        This is similar to ``DataFrame.apply``, except that ``axis=None``
        applies the function to the entire DataFrame at once,
        rather than column-wise or row-wise.

        Examples
        --------
        >>> def highlight_max(x, color):
        ...     return np.where(x == np.nanmax(x.to_numpy()), f"color: {color};", None)
        >>> df = pd.DataFrame(np.random.randn(5, 2), columns=["A", "B"])