docs: def isoratio_init(self,isos):
          '''
          This file returns the isotopic ratio of two isotopes specified
          as iso1 and iso2. The isotopes are given as, e.g.,
          ['Fe',56,'Fe',58] or ['Fe-56','Fe-58'] (for compatibility)
          -> list.
  
          '''
          if len(isos) == 2:
              dumb = []
              dumb = isos[0].split('-')
              dumb.append(isos[1].split('-')[0])
              dumb.append(isos[1].split('-')[1])
              isos = dumb
          ssratio = old_div(self.habu[isos[0].ljust(2).lower() + str(int(isos[1])).rjust(3)], self.habu[isos[2].ljust(2).lower() + str(int(isos[3])).rjust(3)])
          return ssratio