diff --git a/include/core/graph_handler.h b/include/core/graph_handler.h
index b74f8e13..dc221042 100644
--- a/include/core/graph_handler.h
+++ b/include/core/graph_handler.h
@@ -38,12 +38,14 @@ class GraphHandlerObj {
 
     Tensor tensor(Shape dims, int dtype);
 
+    //------ operators
+
+    inline OpVec operators() { return g->getOperators(); }
+
     Tensor conv(Tensor input, Tensor weight, Tensor output, int ph, int pw,
                 int sh, int sw, int dh, int dw);
-
     Tensor matmul(Tensor a, Tensor b, Tensor y, bool transA, bool transB,
                   Tensor bias, ActType act);
-
     Tensor batchNorm(Tensor input, Tensor output, Tensor mean, Tensor var,
                      Tensor scale, Tensor bias, float momentum, float eps,
                      bool training);
@@ -77,6 +79,10 @@ class GraphHandlerObj {
     Tensor pad(Tensor input, Tensor output, const vector<int> &pads,
                const optional<vector<int>> &axes);
 
+    //------ modifiers
+
+    inline bool topo_sort() { return g->topo_sort(); }
+
     //------ runtime
 
     inline void data_malloc() { g->dataMalloc(); }
diff --git a/pyinfinitensor/src/pyinfinitensor/onnx.py b/pyinfinitensor/src/pyinfinitensor/onnx.py
index a429368f..832e398c 100644
--- a/pyinfinitensor/src/pyinfinitensor/onnx.py
+++ b/pyinfinitensor/src/pyinfinitensor/onnx.py
@@ -6,11 +6,11 @@ from functools import reduce
 runtime = backend.cpu_runtime()
 
 
-def from_onnx(model: onnx.ModelProto):
+def from_onnx(model: onnx.ModelProto) -> backend.GraphHandler:
     model = infer_shapes(model)
-    handler = backend.GraphHandlerObj(runtime)
+    handler = backend.GraphHandler(runtime)
 
-    tensors: Dict[str, backend.TensorObj] = dict()
+    tensors: Dict[str, backend.Tensor] = dict()
     data: Dict[str, onnx.TensorProto] = dict()
 
     for input in model.graph.input:
@@ -303,6 +303,13 @@ def from_onnx(model: onnx.ModelProto):
             raise Exception('Unsupported operator "{}"'.format(node.op_type))
 
 
+def to_onnx(graph: backend.GraphHandler):
+    if not graph.topo_sort():
+        raise Exception("Sorting fails")
+
+    ops = graph.operators()
+
+
 def parse_onnx(model: onnx.ModelProto):
     print()
 
diff --git a/pyinfinitensor/tests/test_onnx.py b/pyinfinitensor/tests/test_onnx.py
index 46328f76..9547bcac 100644
--- a/pyinfinitensor/tests/test_onnx.py
+++ b/pyinfinitensor/tests/test_onnx.py
@@ -8,7 +8,7 @@ from onnx.helper import (
     make_tensor_value_info,
 )
 from onnx.checker import check_model
-from pyinfinitensor.onnx import from_onnx, parse_onnx, backend, runtime
+from pyinfinitensor.onnx import from_onnx, parse_onnx, backend, runtime, to_onnx
 
 
 def make_and_import_model(graph: onnx.GraphProto):
@@ -293,12 +293,14 @@ class TestStringMethods(unittest.TestCase):
         parse_onnx(model)
 
     def test_frontend(self):
-        handler = backend.GraphHandlerObj(runtime)
+        handler = backend.GraphHandler(runtime)
         i = handler.tensor([1, 2, 3], 12)
         w = handler.tensor([1, 3, 4], 12)
         o = handler.tensor([1, 2, 4], 12)
         handler.matmul(i, w, o, False, False, None, backend.ActType.Relu)
 
+        to_onnx(handler)
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/src/ffi/ffi_infinitensor.cc b/src/ffi/ffi_infinitensor.cc
index 37b7d5da..b0de6d08 100644
--- a/src/ffi/ffi_infinitensor.cc
+++ b/src/ffi/ffi_infinitensor.cc
@@ -25,17 +25,18 @@ void init_graph_builder(py::module &m) {
     using Handler = GraphHandlerObj;
 
     m.def("cpu_runtime", &CpuRuntimeObj::getInstance);
-    py::class_<RuntimeObj, std::shared_ptr<RuntimeObj>>(m, "RuntimeObj");
+    py::class_<RuntimeObj, std::shared_ptr<RuntimeObj>>(m, "Runtime");
     py::class_<CpuRuntimeObj, std::shared_ptr<CpuRuntimeObj>, RuntimeObj>(
-        m, "CpuRuntimeObj");
+        m, "CpuRuntime");
     py::class_<TensorObj, std::shared_ptr<TensorObj>>(m, "TensorObj");
+    py::class_<OperatorObj, std::shared_ptr<OperatorObj>>(m, "Operator");
     py::enum_<ActType>(m, "ActType")
         .value("Linear", ActType::None) // `None` is Python keyword
         .value("Relu", ActType::Relu)
         .value("Sigmoid", ActType::Sigmoid)
         .value("Tanh", ActType::Tanh)
         .export_values();
-    py::class_<Handler>(m, "GraphHandlerObj")
+    py::class_<Handler>(m, "GraphHandler")
         .def(py::init<Runtime>())
         .def("tensor", py::overload_cast<Shape, int>(&Handler::tensor),
              policy::move)
@@ -103,6 +104,10 @@ void init_graph_builder(py::module &m) {
              py::overload_cast<Tensor, Tensor, const vector<int> &,
                                const optional<vector<int>> &>(&Handler::pad),
              policy::move)
+        .def("topo_sort", py::overload_cast<>(&Handler::topo_sort),
+             policy::automatic)
+        .def("operators", py::overload_cast<>(&Handler::operators),
+             policy::move)
         .def("data_malloc", &Handler::data_malloc, policy::automatic)
         .def("run", &Handler::run, policy::automatic);
 }