code: def add_waveform(self, waveform):
          
          if not isinstance(waveform, PlotWaveform):
              self.log_exc(u"waveform must be an instance of PlotWaveform", None, True, TypeError)
          self.waveform = waveform
          self.log(u"Added waveform")
docs: Add a waveform to the plot.
  
          :param waveform: the waveform to be added
          :type  waveform: :class:`~aeneas.plotter.PlotWaveform`
          :raises: TypeError: if ``waveform`` is not an instance of :class:`~aeneas.plotter.PlotWaveform`