<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def timeline_slider(self, text='Time', ax=None, valfmt=None, color=None):
 """Creates a timeline slider. Parameters text : str, optional The text to display for the slider. Defaults to 'Time' ax : matplotlib.axes.Axes, optional The matplotlib axes to attach the slider to. valfmt : str, optional a format specifier used to print the time Defaults to '%s' for datetime64, timedelta64 and '%1.2f' otherwise. color : The color of the slider. """

        if ax is None:
            adjust_plot = {'bottom': .2}
            rect = [.18, .05, .5, .03]

            plt.subplots_adjust(**adjust_plot)
            self.slider_ax = plt.axes(rect)
        else:
            self.slider_ax = ax

        if valfmt is None:
            if (np.issubdtype(self.timeline.t.dtype, np.datetime64)
               or np.issubdtype(self.timeline.t.dtype, np.timedelta64)):
                valfmt = '%s'
            else:
                valfmt = '%1.2f'

        if self.timeline.log:
            valfmt = '$10^{%s}$' % valfmt

        self.slider = Slider(
            self.slider_ax, text, 0, self.timeline._len-1,
            valinit=0,
            valfmt=(valfmt+self.timeline.units),
            valstep=1, color=color
        )
        self._has_slider = True

        def set_time(t):
            self.timeline.index = int(self.slider.val)
            self.slider.valtext.set_text(
                self.slider.valfmt % (self.timeline[self.timeline.index]))
            if self._pause:
                for block in self.blocks:
                    block._update(self.timeline.index)
                self.fig.canvas.draw()
        self.slider.on_changed(set_time)