code: def label_subplot(ax=None, x=0.5, y=-0.25, text="(a)", **kwargs):
      
      if ax is None:
          ax = plt.gca()
      ax.text(x=x, y=y, s=text, transform=ax.transAxes,
              horizontalalignment="center", verticalalignment="top", **kwargs)
docs: Create a subplot label.