code: def save_signal(self,filename=None):
          
          if filename is None:
              filename = os.path.join(self.folder,'trsig.pkl')
          self.trsig.save(filename)
docs: Saves TransitSignal.
  
          Calls :func:`TransitSignal.save`; default filename is
          ``trsig.pkl`` in ``self.folder``.