[add] Tensor::clone binding and update Tensor display

python_binding/data/pybind_Tensor.cpp

@@ -315,6 +315,7 @@ void init_Tensor(py::module& m){
     .def(py::self - py::self)
     .def(py::self * py::self)
     .def(py::self / py::self)
+    .def("clone", &Tensor::clone)
 	.def("sqrt", &Tensor::sqrt)
     .def("set_datatype", &Tensor::setDataType, py::arg("datatype"), py::arg("copyCast") = true)
     .def("set_backend", &Tensor::setBackend, py::arg("name"), py::arg("device") = 0, py::arg("copyFrom") = true)
@@ -334,8 +335,8 @@ void init_Tensor(py::module& m){
     .def("cpy_transpose", (void (Tensor::*)(const Tensor& src, const std::vector<DimSize_t>& transpose)) &Tensor::copyTranspose, py::arg("src"), py::arg("transpose"))
 
     .def("__str__", [](Tensor& b) {
-        if (b.empty()) {
-            return std::string("{}");
+        if (b.empty() && b.undefined()) {
+                return std::string("{}");
         } else {
             return b.toString();
         }