diff --git a/imperative/python/src/helper.cpp b/imperative/python/src/helper.cpp
index 98d78ea06549dd84be2d5d4ad9a0d9ad0b753edf..7f38403b504c6e09753c551867f67fd0a722f07c 100644
--- a/imperative/python/src/helper.cpp
+++ b/imperative/python/src/helper.cpp
@@ -192,12 +192,16 @@ std::unique_ptr<PyArray_Descr, PyArrayDescrDeleter> dtype_mgb2np_descr(DType dty
                const std::vector<std::pair<const char*, PyObject*>>& data) {
                 PyObject* metadata = PyDict_New();
                 PyObject* mgb_dtype_metadata = PyDict_New();
-                PyDict_SetItemString(
-                        mgb_dtype_metadata, "name", PyUnicode_FromString(name));
+                PyObject* py_name = PyUnicode_FromString(name);
+
+                PyDict_SetItemString(mgb_dtype_metadata, "name", py_name);
+                Py_DECREF(py_name);
+
                 for (const auto& d : data) {
                     PyDict_SetItemString(mgb_dtype_metadata, d.first, d.second);
                 }
                 PyDict_SetItemString(metadata, "mgb_dtype", mgb_dtype_metadata);
+                Py_DECREF(mgb_dtype_metadata);
                 return metadata;
             };
     if (dtype.has_param()) {
@@ -206,51 +210,62 @@ std::unique_ptr<PyArray_Descr, PyArrayDescrDeleter> dtype_mgb2np_descr(DType dty
             case DTypeEnum::QuantizedS1: {
                 auto& param = dtype.param<dtype::QuantizedS1>();
                 type_descr = PyArray_DescrNewFromType(NPY_INT8);
+                PyObject* scale = PyFloat_FromDouble(param.scale);
                 type_descr->metadata = build_mgb_dtype_dict(
-                        DTypeTrait<dtype::QuantizedS1>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)}});
+                        DTypeTrait<dtype::QuantizedS1>::name, {{"scale", scale}});
+                Py_DECREF(scale);
                 break;
             }
             case DTypeEnum::Quantized4Asymm: {
                 auto& param = dtype.param<dtype::Quantized4Asymm>();
                 type_descr = PyArray_DescrNewFromType(NPY_UINT8);
+                PyObject* scale = PyFloat_FromDouble(param.scale);
+                PyObject* zero_point = PyLong_FromLong(param.zero_point);
                 type_descr->metadata = build_mgb_dtype_dict(
                         DTypeTrait<dtype::Quantized4Asymm>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)},
-                         {"zero_point", PyLong_FromLong(param.zero_point)}});
+                        {{"scale", scale}, {"zero_point", zero_point}});
+                Py_DECREF(scale);
+                Py_DECREF(zero_point);
                 break;
             }
             case DTypeEnum::QuantizedS4: {
                 auto& param = dtype.param<dtype::QuantizedS4>();
                 type_descr = PyArray_DescrNewFromType(NPY_INT8);
+                PyObject* scale = PyFloat_FromDouble(param.scale);
                 type_descr->metadata = build_mgb_dtype_dict(
-                        DTypeTrait<dtype::QuantizedS4>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)}});
+                        DTypeTrait<dtype::QuantizedS4>::name, {{"scale", scale}});
+                Py_DECREF(scale);
                 break;
             }
             case DTypeEnum::Quantized8Asymm: {
                 auto& param = dtype.param<dtype::Quantized8Asymm>();
                 type_descr = PyArray_DescrNewFromType(NPY_UINT8);
+                PyObject* scale = PyFloat_FromDouble(param.scale);
+                PyObject* zero_point = PyLong_FromLong(param.zero_point);
                 type_descr->metadata = build_mgb_dtype_dict(
                         DTypeTrait<dtype::Quantized8Asymm>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)},
-                         {"zero_point", PyLong_FromLong(param.zero_point)}});
+                        {{"scale", scale}, {"zero_point", zero_point}});
+                Py_DECREF(scale);
+                Py_DECREF(zero_point);
                 break;
             }
             case DTypeEnum::QuantizedS8: {
                 auto& param = dtype.param<dtype::QuantizedS8>();
                 type_descr = PyArray_DescrNewFromType(NPY_INT8);
-                type_descr->metadata = build_mgb_dtype_dict(
-                        DTypeTrait<dtype::QuantizedS8>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)}});
+                PyObject* scale = PyFloat_FromDouble(param.scale);
+                auto metadata = build_mgb_dtype_dict(
+                        DTypeTrait<dtype::QuantizedS8>::name, {{"scale", scale}});
+                type_descr->metadata = metadata;
+                Py_DECREF(scale);
                 break;
             }
             case DTypeEnum::QuantizedS32: {
                 auto& param = dtype.param<dtype::QuantizedS32>();
                 type_descr = PyArray_DescrNewFromType(NPY_INT32);
+                PyObject* scale = PyFloat_FromDouble(param.scale);
                 type_descr->metadata = build_mgb_dtype_dict(
-                        DTypeTrait<dtype::QuantizedS32>::name,
-                        {{"scale", PyFloat_FromDouble(param.scale)}});
+                        DTypeTrait<dtype::QuantizedS32>::name, {{"scale", scale}});
+                Py_DECREF(scale);
                 break;
             }
             default:
diff --git a/imperative/python/src/tensor_utils.cpp b/imperative/python/src/tensor_utils.cpp
index 906615f5d3c42c65276102ea4962e652b7ae213f..19a2f3f7d1e211ce1a2a0135634ae702e6995882 100644
--- a/imperative/python/src/tensor_utils.cpp
+++ b/imperative/python/src/tensor_utils.cpp
@@ -422,6 +422,7 @@ mgb::DType _get_dtype(py::handle tensor) {
 
 py::object _astype_cpp(py::handle tensor, py::handle dtype_hdl) {
     PyArray_Descr* descr;
+    py::object ret;
     if (!PyArray_DescrConverter(dtype_hdl.ptr(), &descr)) {
         throw py::value_error(ssprintf(
                 "can not convert to numpy.dtype from %s",
@@ -432,11 +433,13 @@ py::object _astype_cpp(py::handle tensor, py::handle dtype_hdl) {
         std::shared_ptr<OpDef> op = TypeCvt::make(npy::dtype_np2mgb_descr(descr));
         py::object Op = py::cast(op);
         PyObject* p[2] = {Op.ptr(), tensor.ptr()};
-        py::tuple ret = py::reinterpret_steal<py::object>(py_apply(NULL, p, 2));
-        return ret[0];
+        py::tuple apply_res = py::reinterpret_steal<py::object>(py_apply(NULL, p, 2));
+        ret = apply_res[0];
     } else {
-        return py::reinterpret_borrow<py::object>(tensor);
+        ret = py::reinterpret_borrow<py::object>(tensor);
     }
+    Py_DECREF(descr);
+    return ret;
 }
 
 py::object _convert_single_value_cpp(