group op has list rather than tuple
@@ -95,7 +95,7 @@ class NatGradOptimizer(optimizer.Optimizer):
q_mu, q_sqrt = arg[:2]
xi_transform = arg[2] if len(arg) > 2 else XiNat()
ops.append(self._build_natgrad_step_op(q_mu, q_sqrt, xi_transform))
- ops = list(sum(ops, ()))
+ ops = list(sum(ops, []))
return tf.group(ops)
def _build_natgrad_step_op(self, q_mu_param, q_sqrt_param, xi_transform):
