expose GradOpMaker to Python

paddle/pybind/pybind.cc

@@ -282,15 +282,22 @@ All parameter, weight, gradient are variables in Paddle.
     }
     return ret_values;
   });
-  m.def("get_grad_op_desc",
+  m.def("get_grad_op_descs",
         [](const OpDescBind &op_desc,
            const std::unordered_set<std::string> &no_grad_set,
            std::unordered_map<std::string, std::string> &grad_to_var,
            const std::vector<BlockDescBind *> &grad_sub_block) {
-          return framework::OpInfoMap::Instance()
+          std::vector<std::unique_ptr<OpDescBind>> grad_op_descs =
+              framework::OpInfoMap::Instance()
                   .Get(op_desc.Type())
                   .GradOpMaker()(op_desc, no_grad_set, &grad_to_var,
                                  grad_sub_block);
+          std::vector<OpDescBind *> grad_op_desc_ptrs(grad_op_descs.size());
+          std::transform(
+              grad_op_descs.begin(), grad_op_descs.end(),
+              grad_op_desc_ptrs.begin(),
+              [](std::unique_ptr<OpDescBind> &p) { return p.release(); });
+          return grad_op_desc_ptrs;
         });
   m.def("prune", [](const ProgramDescBind &origin,
                     const std::vector<std::array<size_t, 2>> &targets) {