def _get_roots(cls, method, poly, radicals):
        """Return postprocessed roots of specified kind. """
        if not poly.is_univariate:
            raise PolynomialError("only univariate polynomials are allowed")

        coeff, poly = cls._preprocess_roots(poly)
        roots = []

        for root in getattr(cls, method)(poly):
            roots.append(coeff*cls._postprocess_root(root, radicals))

        return roots

    def _real_roots(cls, poly):
        """Get real roots of a composite polynomial. """
        factors = _pure_factors(poly)

        reals = cls._get_reals(factors)
        reals_count = cls._count_roots(reals)

        roots = []

        for index in range(0, reals_count):
            roots.append(cls._reals_index(reals, index))

        return roots

    def _real_roots(cls, poly):
        """Get real roots of a composite polynomial. """
        (_, factors) = poly.factor_list()

        reals = cls._get_reals(factors)
        reals = cls._reals_sorted(reals)
        reals_count = cls._count_roots(reals)

        roots = []

        for index in range(0, reals_count):
            roots.append(cls._reals_index(reals, index))

        return roots

    def _all_roots(cls, poly, use_cache=True):
        """Get real and complex roots of a composite polynomial. """
        factors = _pure_factors(poly)

        reals = cls._get_reals(factors, use_cache=use_cache)
        reals_count = cls._count_roots(reals)

        roots = []

        for index in range(0, reals_count):
            roots.append(cls._reals_index(reals, index))

        complexes = cls._get_complexes(factors, use_cache=use_cache)
        complexes_count = cls._count_roots(complexes)

        for index in range(0, complexes_count):
            roots.append(cls._complexes_index(complexes, index))

        return roots