    should only be used with linear scales; It has no clear meaning for
        all other scales, and thus the behavior is undefined. Please specify
        the line using the points *xy1*, *xy2* for non-linear scales.

        The *transform* keyword argument only applies to the points *xy1*,
        *xy2*. The *slope* (if given) is always in data coordinates. This can
        be used e.g. with ``ax.transAxes`` for drawing grid lines with a fixed
        slope.

        Parameters
        ----------
        xy1, xy2 : (float, float)
            Points for the line to pass through.
            Either *xy2* or *slope* has to be given.
        slope : float, optional
            The slope of the line. Either *xy2* or *slope* has to be given.

        Returns
        -------
        `.Line2D`

        Other Parameters
        ----------------
        **kwargs
            Valid kwargs are `.Line2D` properties

            %(Line2D:kwdoc)s

        See Also
        --------
        axhline : for horizontal lines
        axvline : for vertical lines

        Examples
        --------
        Draw a thick red line passing through (0, 0) and (1, 1)::

            >>> axline((0, 0), (1, 1), linewidth=4, color='r')
        N