support `numpy.array/asarray(tensor) -> ndarray`, test=develop (#32300)

python/paddle/fluid/dygraph/varbase_patch_methods.py

@@ -434,6 +434,9 @@ def monkey_patch_varbase():
     def __bool__(self):
         return self.__nonzero__()
 
+    def __array__(self, dtype=None):
+        return self.numpy().astype(dtype)
+
     for method_name, method in (
         ("__bool__", __bool__), ("__nonzero__", __nonzero__),
         ("_to_static_var", _to_static_var), ("set_value", set_value),
@@ -442,7 +445,7 @@ def monkey_patch_varbase():
         ("gradient", gradient), ("register_hook", register_hook),
         ("__str__", __str__), ("__repr__", __str__),
         ("__deepcopy__", __deepcopy__), ("__module__", "paddle"),
-        ("__name__", "Tensor")):
+        ("__name__", "Tensor"), ("__array__", __array__)):
         setattr(core.VarBase, method_name, method)
 
     # NOTE(zhiqiu): pybind11 will set a default __str__ method of enum class.

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

@@ -502,6 +502,15 @@ class TestVarBase(unittest.TestCase):
                 np.array_equal(var.numpy(),
                                fluid.framework._var_base_to_np(var)))
 
+    def test_var_base_as_np(self):
+        with fluid.dygraph.guard():
+            var = fluid.dygraph.to_variable(self.array)
+            self.assertTrue(np.array_equal(var.numpy(), np.array(var)))
+            self.assertTrue(
+                np.array_equal(
+                    var.numpy(), np.array(
+                        var, dtype=np.float32)))
+
     def test_if(self):
         with fluid.dygraph.guard():
             var1 = fluid.dygraph.to_variable(np.array([[[0]]]))