def _eval_evalf(self, prec):
        # The default code is insufficient for polar arguments.
        # mpmath provides an optional argument "r", which evaluates
        # G(z**(1/r)). I am not sure what its intended use is, but we hijack it
        # here in the following way: to evaluate at a number z of |argument|
        # less than (say) n*pi, we put r=1/n, compute z' = root(z, n)
        # (carefully so as not to loose the branch information), and evaluate
        # G(z'**(1/r)) = G(z'**n) = G(z).
        from sympy.functions import exp_polar, ceiling
        from sympy import Expr
        import mpmath
        z = self.argument
        znum = self.argument._eval_evalf(prec)
        if znum.has(exp_polar):
            znum, branch = znum.as_coeff_mul(exp_polar)
            if len(branch) != 1:
                return
            branch = branch[0].args[0]/I
        else:
            branch = S(0)
        n = ceiling(abs(branch/S.Pi)) + 1
        znum = znum**(S(1)/n)*exp(I*branch / n)

        # Convert all args to mpf or mpc
        try:
            [z, r, ap, bq] = [arg._to_mpmath(prec)
                    for arg in [znum, 1/n, self.args[0], self.args[1]]]
        except __HOLE__:
            return

        with mpmath.workprec(prec):
            v = mpmath.meijerg(ap, bq, z, r)

        return Expr._from_mpmath(v, prec)
dataset/ETHPy150Open sympy/sympy/sympy/functions/special/hyper.py/meijerg._eval_evalf