API(to_variable/save_dygraph) error message enhancement(#23683)

* API(to_variable/save_dygraph) error message enhancement

python/paddle/fluid/dygraph/base.py

@@ -540,4 +540,5 @@ def to_variable(value, name=None, zero_copy=None):
         return value
     else:
         raise TypeError(
-            "to_variable only accepts 'ndarray' and 'Variable' as value's input")
+            "The type of input value is invalid, expected type is 'ndarray' or 'Variable', but received %s"
+            % type(value))

python/paddle/fluid/dygraph/checkpoint.py

@@ -63,7 +63,7 @@ def save_dygraph(state_dict, model_path):
     '''
 
     base_name = os.path.basename(model_path)
-    assert base_name != "", "model_path MUST be format of dirname/filename [dirname\\filename in Window], Now filename is empty str"
+    assert base_name != "", "The input model_path MUST be format of dirname/filename [dirname\\filename in Windows system], but received filename is empty string."
 
     suffix = ".pdparams"
     assert len(state_dict) > 0, "state_dict is empty, no need to save"

python/paddle/fluid/layer_helper_base.py

@@ -81,8 +81,8 @@ class LayerHelperBase(object):
             return value
         else:
             raise TypeError(
-                "to_variable only accepts 'ndarray' or 'Variable' or 'VarBase' as value's input"
-            )
+                "The type of input value is invalid, expected type is 'ndarray' or 'Variable', but received %s"
+                % type(value))
 
     def _create_weight_normalize(self, attr, shape, dtype):
         from .layers import elementwise_mul, elementwise_div, reshape

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

@@ -39,6 +39,13 @@ class TestVarBase(unittest.TestCase):
             self.assertEqual(var.shape, self.shape)
             self.assertEqual(var.dtype, core.VarDesc.VarType.FP32)
             self.assertEqual(var.type, core.VarDesc.VarType.LOD_TENSOR)
+            # The type of input must be 'ndarray' or 'Variable', it will raise TypeError
+            with self.assertRaises(TypeError):
+                var = fluid.dygraph.to_variable("test", name="abc")
+            # test to_variable of LayerObjectHelper(LayerHelperBase)
+            with self.assertRaises(TypeError):
+                linear = fluid.dygraph.Linear(32, 64)
+                var = linear._helper.to_variable("test", name="abc")
 
     def test_write_property(self):
         with fluid.dygraph.guard():