docs: def iso_abundance(self,isos):
          '''
          This routine returns the abundance of a specific isotope.
          Isotope given as, e.g., 'Si-28' or as list
          ['Si-28','Si-29','Si-30']
  
          '''
          if type(isos) == list:
              dumb = []
              for it in range(len(isos)):
                  dumb.append(isos[it].split('-'))
              ssratio = []
              isos = dumb
              for it in range(len(isos)):
                  ssratio.append(self.habu[isos[it][0].ljust(2).lower() + str(int(isos[it][1])).rjust(3)])
          else:
              isos = isos.split('-')
              ssratio = self.habu[isos[0].ljust(2).lower() + str(int(isos[1])).rjust(3)]
          return ssratio