Fix api for ErrorClipByValue, code demo of clip_by_norm. test=develop (#27654)

* Fix ErrorClipByValue api and demo code of clip_by_value. test=develop
Co-authored-by: Ntianshuo78520a <707759223@qq.com>

python/paddle/fluid/layers/nn.py

@@ -12415,12 +12415,17 @@ def clip_by_norm(x, max_norm, name=None):
     Examples:
         .. code-block:: python
 
-            import paddle.fluid as fluid
-            input = fluid.data(
-                name='data', shape=[None, 1], dtype='float32')
-            reward = fluid.layers.clip_by_norm(x=input, max_norm=1.0)
+            import paddle
+            import numpy as np
+
+            paddle.disable_static()
+            input = paddle.to_tensor(data=np.array([[0.1, 0.2], [0.3, 0.4]]), dtype="float32")
+            reward = paddle.nn.clip_by_norm(x=input, max_norm=1.0)
     """
 
+    if in_dygraph_mode():
+        return core.ops.clip_by_norm(x, 'max_norm', max_norm)
+
     helper = LayerHelper("clip_by_norm", **locals())
     check_variable_and_dtype(x, 'X', ['float32'], 'clip_by_norm')
     check_type(max_norm, 'max_norm', (float), 'clip_by_norm')

python/paddle/nn/__init__.py

@@ -31,7 +31,6 @@ __all__ += rnn.__all__
 __all__ += weight_norm_hook.__all__
 
 # TODO: define alias in nn directory
-# from .clip import ErrorClipByValue        #DEFINE_ALIAS
 from .clip import GradientClipByGlobalNorm  #DEFINE_ALIAS
 from .clip import GradientClipByNorm  #DEFINE_ALIAS
 from .clip import GradientClipByValue  #DEFINE_ALIAS