code: def show_label(self, text, size = None, color = None, font_desc = None):
          
          font_desc = pango.FontDescription(font_desc or _font_desc)
          if color: self.set_color(color)
          if size: font_desc.set_absolute_size(size * pango.SCALE)
          self.show_layout(text, font_desc)
docs: display text. unless font_desc is provided, will use system's default font