[Eager] Fix numpy interface for constructing empty tensor (#41904) (#41954)

* [Eager] Fix numpy interface for constructing empty tensor

* Fix CI, construct empty tensor

* Modify empty tensor's shape from [] to [0]

* Add more test for constructing empty tensor

paddle/fluid/pybind/eager.cc

@@ -62,7 +62,7 @@ void EmptyTensorInitializer(TensorObject* self, const std::string& name,
                             bool persistable = false, int stop_gradient = -1,
                             framework::proto::VarType::Type dtype =
                                 paddle::framework::proto::VarType::FP32,
-                            const std::vector<int>& dims = {},
+                            const std::vector<int>& dims = {0},
                             framework::proto::VarType::Type var_type =
                                 paddle::framework::proto::VarType::LOD_TENSOR) {
   auto ddims = phi::make_ddim(dims);
@@ -75,7 +75,7 @@ void EmptyTensorInitializer(TensorObject* self, const std::string& name,
   if (var_type == paddle::framework::proto::VarType::LOD_TENSOR) {
     // TODO(jiabin): Maybe support LOD later
     std::shared_ptr<phi::DenseTensor> dense_tensor = nullptr;
-    if (dims.empty()) {
+    if (dims.size() == 1 && dims[0] == 0) {
       std::shared_ptr<phi::Allocation> allocation_ptr = nullptr;
       dense_tensor = std::make_shared<phi::DenseTensor>(
           allocation_ptr,

paddle/fluid/pybind/eager_method.cc

@@ -194,6 +194,17 @@ static PyObject* tensor_method_numpy(TensorObject* self, PyObject* args,
       nullptr);
 
   if (!self->tensor.impl()->initialized()) {
+    if (tensor_dims.size() == 0) {
+      py_dims[0] = 0;
+      py_strides[0] = 0;
+      PyObject* array = api.PyArray_NewFromDescr_(
+          api.PyArray_Type_, api.PyArray_DescrFromType_(numpy_dtype), 1,
+          py_dims, py_strides, nullptr,
+          pybind11::detail::npy_api::NPY_ARRAY_ALIGNED_ |
+              pybind11::detail::npy_api::NPY_ARRAY_WRITEABLE_,
+          nullptr);
+      return array;
+    }
     return array;
   }
 

paddle/phi/api/lib/tensor.cc

@@ -114,9 +114,6 @@ phi::DDim Tensor::dims() const { return impl_->dims(); }
 
 std::vector<int64_t> Tensor::shape() const {
   auto dims = impl_->dims();
-  if (dims.size() == 1 && dims.at(0) == 0) {
-    return {};
-  }
   return phi::vectorize<int64_t>(dims);
 }
 

python/paddle/fluid/tests/unittests/test_egr_python_api.py

@@ -114,7 +114,7 @@ class EagerVariablePropertiesAndMethodsTestCase(unittest.TestCase):
         egr_tensor = core.eager.Tensor()
         self.assertEqual(egr_tensor.persistable, False)
         self.assertTrue("generated" in egr_tensor.name)
-        self.assertEqual(egr_tensor.shape, [])
+        self.assertEqual(egr_tensor.shape, [0])
         self.assertEqual(egr_tensor.dtype, core.VarDesc.VarType.FP32)
         self.assertEqual(egr_tensor.stop_gradient, True)
 

python/paddle/fluid/tests/unittests/test_var_base.py

@@ -214,6 +214,13 @@ class TestVarBase(unittest.TestCase):
                 self.assertEqual(x.item(), 1 + 1j)
                 self.assertTrue(isinstance(x.item(), complex))
 
+                # empty tensor
+                x = paddle.to_tensor([])
+                self.assertEqual(x.shape, [0])
+                expected_result = np.array([], dtype='float32')
+                self.assertEqual(x.numpy().shape, expected_result.shape)
+                self.assertTrue(np.array_equal(x.numpy(), expected_result))
+
                 numpy_array = np.random.randn(3, 4)
                 # covert core.LoDTensor to paddle.Tensor
                 lod_tensor = paddle.fluid.core.LoDTensor()