code: def show_letter(
              self,
              s,
              text_colour=[255, 255, 255],
              back_colour=[0, 0, 0]
          ):
          
  
          if len(s) > 1:
              raise ValueError('Only one character may be passed into this method')
          # We must rotate the pixel map left through 90 degrees when drawing
          # text, see _load_text_assets
          previous_rotation = self._rotation
          self._rotation -= 90
          if self._rotation < 0:
              self._rotation = 270
          dummy_colour = [None, None, None]
          pixel_list = [dummy_colour] * 8
          pixel_list.extend(self._get_char_pixels(s))
          pixel_list.extend([dummy_colour] * 16)
          coloured_pixels = [
              text_colour if pixel == [255, 255, 255] else back_colour
              for pixel in pixel_list
          ]
          self.set_pixels(coloured_pixels)
          self._rotation = previous_rotation
docs: Displays a single text character on the LED matrix using the specified
          colours