code: def plot(message, duration=1, ax=None):
      
      lst_bin = _encode_binary(message)
      x, y = _create_x_y(lst_bin, duration)
      ax = _create_ax(ax)
      ax.plot(x, y, linewidth=2.0)
      delta_y = 0.1
      ax.set_ylim(-delta_y, 1 + delta_y)
      ax.set_yticks([0, 1])
      delta_x = 0.5 * duration
      ax.set_xlim(-delta_x, len(lst_bin) * duration + delta_x)
      return ax
docs: Plot a message
  
      Returns: ax a Matplotlib Axe