[Cpp Extension] return Py_None if Tensor not initialized (#50745)

* [Cpp Extension] return Py_None if Tensor not initialized

* fix jit test

paddle/utils/pybind.h

@@ -69,7 +69,8 @@ struct type_caster<paddle::experimental::Tensor> {
   static handle cast(const paddle::experimental::Tensor& src,
                      return_value_policy /* policy */,
                      handle /* parent */) {
-    return handle(paddle::pybind::ToPyObject(src));
+    return handle(paddle::pybind::ToPyObject(
+        src, true /* return_py_none_if_not_initialize */));
   }
 };
 }  // namespace detail

python/paddle/fluid/tests/cpp_extension/cpp_extension_setup.py

@@ -25,13 +25,14 @@ for site_packages_path in getsitepackages():
     paddle_includes.append(
         os.path.join(site_packages_path, 'paddle', 'include', 'third_party')
     )
+# Add current dir, search custom_power.h
+paddle_includes.append(os.path.dirname(os.path.abspath(__file__)))
 
 setup(
     name='custom_cpp_extension',
     ext_modules=CppExtension(
-        sources=["custom_add.cc", "custom_sub.cc"],
-        include_dirs=paddle_includes
-        + [os.path.dirname(os.path.abspath(__file__))],
+        sources=["custom_extension.cc", "custom_sub.cc"],
+        include_dirs=paddle_includes,
         extra_compile_args={'cc': ['-w', '-g']},
         verbose=True,
     ),

python/paddle/fluid/tests/cpp_extension/custom_add.cc → python/paddle/fluid/tests/cpp_extension/custom_extension.cc

@@ -24,9 +24,18 @@ paddle::Tensor custom_add(const paddle::Tensor& x, const paddle::Tensor& y) {
   return paddle::add(paddle::exp(x), paddle::exp(y));
 }
 
+paddle::Tensor nullable_tensor(bool return_none = false) {
+  paddle::Tensor t;
+  if (!return_none) {
+    t = paddle::ones({2, 2});
+  }
+  return t;
+}
+
 PYBIND11_MODULE(custom_cpp_extension, m) {
   m.def("custom_add", &custom_add, "exp(x) + exp(y)");
   m.def("custom_sub", &custom_sub, "exp(x) - exp(y)");
+  m.def("nullable_tensor", &nullable_tensor, "returned Tensor might be None");
 
   py::class_<Power>(m, "Power")
       .def(py::init<int, int>())

python/paddle/fluid/tests/cpp_extension/test_cpp_extension_jit.py

@@ -27,7 +27,7 @@ if os.name == 'nt' or sys.platform.startswith('darwin'):
     exit()
 
 # Compile and load cpp extension Just-In-Time.
-sources = ["custom_add.cc", "custom_sub.cc"]
+sources = ["custom_extension.cc", "custom_sub.cc"]
 paddle_includes = []
 for site_packages_path in getsitepackages():
     paddle_includes.append(

python/paddle/fluid/tests/cpp_extension/test_cpp_extension_setup.py

@@ -148,6 +148,7 @@ class TestCppExtensionSetupInstall(unittest.TestCase):
         self._test_extension_function_plain()
         self._test_extension_function_mixed()
         self._test_extension_class()
+        self._test_nullable_tensor()
         # Custom op
         self._test_static()
         self._test_dynamic()
@@ -213,6 +214,19 @@ class TestCppExtensionSetupInstall(unittest.TestCase):
                 atol=1e-5,
             )
 
+    def _test_nullable_tensor(self):
+        import custom_cpp_extension
+
+        x = custom_cpp_extension.nullable_tensor(True)
+        assert x is None, "Return None when input parameter return_none = True"
+        x = custom_cpp_extension.nullable_tensor(False).numpy()
+        x_np = np.ones(shape=[2, 2])
+        np.testing.assert_array_equal(
+            x,
+            x_np,
+            err_msg='extension out: {},\n numpy out: {}'.format(x, x_np),
+        )
+
     def _test_static(self):
         import mix_relu_extension