[Dy2Stat] Support grammar: for ele in var[idx] (#29541)

Support to transformfor ele in var stms in which var is a slice of Tensor.

python/paddle/fluid/dygraph/dygraph_to_static/utils.py

@@ -882,6 +882,8 @@ class ForNodeVisitor(object):
                 self.node.iter.func,
                 gast.Attribute) and self.node.iter.func.attr == 'numpy':
             return True
+        elif isinstance(self.node.iter, gast.Subscript):
+            return True
         else:
             return False
 

python/paddle/fluid/tests/unittests/dygraph_to_static/test_for_enumerate.py

@@ -159,6 +159,7 @@ def for_enumerate_var_numpy_with_start_continue(x_array):
 def for_iter_var(x_array):
     z = fluid.layers.fill_constant([1], 'int32', 0)
     x_array = fluid.dygraph.to_variable(x_array)
+
     for x in x_array:
         z = z + x
     return z
@@ -221,6 +222,17 @@ def for_enumerate_var_with_nested_range(x_array):
     return x
 
 
+# 16. for iter var[idx]
+@paddle.jit.to_static
+def for_iter_var_idx(x_array):
+    z = fluid.layers.fill_constant([1], 'int32', 0)
+    x_array = fluid.dygraph.to_variable(x_array)
+
+    for x in x_array[0:]:
+        z = z + x
+    return z
+
+
 class TestTransformBase(unittest.TestCase):
     def setUp(self):
         self.place = fluid.CUDAPlace(0) if fluid.is_compiled_with_cuda(
@@ -343,6 +355,11 @@ class TestForIterVar(TestForIterVarNumpy):
         self.dygraph_func = for_iter_var
 
 
+class TestForIterVarIdx(TestForIterVarNumpy):
+    def set_test_func(self):
+        self.dygraph_func = for_iter_var_idx
+
+
 class TestForEnumerateVar(TestForIterVarNumpy):
     def set_test_func(self):
         self.dygraph_func = for_enumerate_var