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