优化LayerList类的insert函数

python/paddle/nn/layer/container.py

@@ -626,11 +626,14 @@ def insert(self, index: int, sublayer: Layer) -> None:
                 >>> print(linears[-2] is another)
                 True
         """
-        assert isinstance(index, int) and -len(self._sub_layers) <= index < len(
+        assert isinstance(index, int) and -len(
             self._sub_layers
-        ), f"index should be an integer in range [{-len(self)}, {len(self)})"
+        ) <= index <= len(
+            self._sub_layers
+        ), f"index should be an integer in range [{-len(self)}, {len(self)}]"
 
-        index = self._get_abs_idx(index)
+        if index < 0:
+            index += len(self)
         for i in range(len(self._sub_layers), index, -1):
             self._sub_layers[str(i)] = self._sub_layers[str(i - 1)]
         self._sub_layers[str(index)] = sublayer

test/legacy_test/test_layerlist.py

@@ -0,0 +1,51 @@
+#   Copyright (c) 2025 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+
+import paddle
+
+
+class TestLayerListEmptyInsert(unittest.TestCase):
+    def test_insert_empty_list(self):
+
+        # Test successful case - insert at index 0
+        layers = paddle.nn.LayerList()
+        linear = paddle.nn.Linear(10, 10)
+        try:
+            layers.insert(0, linear)
+            self.assertEqual(len(layers), 1)
+            self.assertTrue(layers[0] is linear)
+        except Exception as e:
+            self.fail(f"Insert at index 0 raised unexpected exception: {e}")
+
+        # Test failure case - insert at index 1
+        layers = paddle.nn.LayerList()
+        with self.assertRaises(AssertionError):
+            layers.insert(1, paddle.nn.Linear(10, 10))
+
+        # Test successful case - insert at index 1 of non-empty list
+        linear1 = paddle.nn.Linear(15, 15)
+        linear2 = paddle.nn.Linear(20, 20)
+        layers = paddle.nn.LayerList([linear1])
+        try:
+            layers.insert(1, linear2)
+            self.assertEqual(len(layers), 2)
+            self.assertTrue(layers[1] is linear2)
+        except Exception as e:
+            self.fail(f"Insert at index 1 raised unexpected exception: {e}")
+
+
+if __name__ == "__main__":
+    unittest.main()