supports string var lod_level property (#39077)

python/paddle/fluid/framework.py

@@ -1763,7 +1763,10 @@ class Variable(object):
         Examples:
           .. code-block:: python
 
+            import paddle
             import paddle.fluid as fluid
+
+            paddle.enable_static()
             cur_program = fluid.Program()
             cur_block = cur_program.current_block()
             new_variable = cur_block.create_var(name="X",
@@ -1773,7 +1776,8 @@ class Variable(object):
         """
         if self.type == core.VarDesc.VarType.SELECTED_ROWS:
             raise Exception("SelectedRows DO NOT supprt lod")
-
+        if self.type == core.VarDesc.VarType.STRINGS:
+            return None
         return self.desc.lod_level()
 
     @property

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

@@ -63,6 +63,12 @@ class TestVariable(unittest.TestCase):
         self.assertRaises(ValueError,
                           lambda: b.create_var(name="fc.w", shape=(24, 100)))
 
+        w = b.create_var(
+            dtype=paddle.fluid.core.VarDesc.VarType.STRINGS,
+            shape=[1],
+            name="str_var")
+        self.assertEqual(None, w.lod_level)
+
     def test_element_size(self):
         with fluid.program_guard(Program(), Program()):
             x = paddle.static.data(name='x1', shape=[2], dtype='bool')