code: def annotate_subplot(ax, ncols=1, nrows=1, letter='a',
                       linear_offset=0.075, fontsize=8):
      '''add a subplot annotation number'''
      ax.text(-ncols*linear_offset, 1+nrows*linear_offset, letter,
          horizontalalignment='center',
          verticalalignment='center',
          fontsize=fontsize, fontweight='demibold',
          transform=ax.transAxesf annotate_subplot(ax, ncols=1, nrows=1, letter='a',
                       linear_offset=0.075, fontsize=8):
      '''add a subplot annotation number'''
      ax.text(-ncols*linear_offset, 1+nrows*linear_offset, letter,
          horizontalalignment='center',
          verticalalignment='center',
          fontsize=fontsize, fontweight='demibold',
          transform=ax.transAxes)
docs: add a subplot annotation number