[API 2.0] Fix example code of api 'switch_case' and add/delete alias (#27578)

* Fix example code of api `fluid.layers.switch_case` to use api2.0

* delete `paddle.nn.switch_case` alias and add `paddle.static.nn.switch_case`

python/paddle/fluid/layers/control_flow.py

@@ -3609,18 +3609,18 @@ def switch_case(branch_index, branch_fns, default=None, name=None):
     This operator is like a C++ switch/case statement.
 
     Args:
-        branch_index(Variable): A Tensor with shape [1] to specify which branch to execute. The data type is ``int32``, ``int64`` or ``uint8``.
+        branch_index(Tensor): A Tensor with shape [1] to specify which branch to execute. The data type is ``int32``, ``int64`` or ``uint8``.
         branch_fns(dict|list|tuple): If it's a list or tuple, the elements in it could be pairs of (int, callable) or simple callables whose actual index will be used as the index of callable. If it's a dict, its key is a python integer and the value is a callable. All callables return the same structure of Tensors.
         default(callable, optional): Callable that returns a structure of Tensors.
         name(str, optional): The default value is None. Normally there is no need for user to set this property. For more information, please refer to :ref:`api_guide_Name`.
 
     Returns:
-        Variable|list(Variable): Tensors returned by the callable specified by ``branch_index`` in ``branch_fns``,
+        Tensor|list(Tensor): Tensors returned by the callable specified by ``branch_index`` in ``branch_fns``,
         or Tensors returned by ``default`` if ``default`` is not None and no index matches in ``branch_fns``,
         or Tensors returned by the callable with the max index in ``branch_fns`` if ``default`` is None and no index matches in ``branch_fns``.
 
     Raises:
-        TypeError: If the type of ``branch_index`` is not Variable.
+        TypeError: If the type of ``branch_index`` is not Tensor.
         TypeError: If the data type of ``branch_index`` is not ``int32``, ``int64`` or ``uint8``.
         TypeError: If the type of ``branch_fns`` is not dict, list or tuple.
         TypeError: If the elements of ``branch_fns`` is not 2-tuple.
@@ -3632,40 +3632,41 @@ def switch_case(branch_index, branch_fns, default=None, name=None):
     Examples:
         .. code-block:: python
 
-            import paddle.fluid as fluid
-            import paddle.fluid.layers as layers
+            import paddle
+
+            paddle.enable_static()
 
             def fn_1():
-                return layers.fill_constant(shape=[1, 2], dtype='float32', value=1)
+                return paddle.fill_constant(shape=[1, 2], dtype='float32', value=1)
 
             def fn_2():
-                return layers.fill_constant(shape=[2, 2], dtype='int32', value=2)
+                return paddle.fill_constant(shape=[2, 2], dtype='int32', value=2)
 
             def fn_3():
-                return layers.fill_constant(shape=[3], dtype='int32', value=3)
+                return paddle.fill_constant(shape=[3], dtype='int32', value=3)
 
-            main_program = fluid.default_startup_program()
-            startup_program = fluid.default_main_program()
-            with fluid.program_guard(main_program, startup_program):
-                index_1 = layers.fill_constant(shape=[1], dtype='int32', value=1)
-                index_2 = layers.fill_constant(shape=[1], dtype='int32', value=2)
+            main_program = paddle.static.default_startup_program()
+            startup_program = paddle.static.default_main_program()
+            with paddle.static.program_guard(main_program, startup_program):
+                index_1 = paddle.fill_constant(shape=[1], dtype='int32', value=1)
+                index_2 = paddle.fill_constant(shape=[1], dtype='int32', value=2)
 
-                out_1 = layers.switch_case(
+                out_1 = paddle.static.nn.switch_case(
                     branch_index=index_1,
                     branch_fns={1: fn_1, 2: fn_2},
                     default=fn_3)
 
-                out_2 = layers.switch_case(
+                out_2 = paddle.static.nn.switch_case(
                     branch_index=index_2,
                     branch_fns=[(1, fn_1), (2, fn_2)],
                     default=fn_3)
 
                 # Argument default is None and no index matches. fn_3 will be called because of the max index 7.
-                out_3 = layers.switch_case(
+                out_3 = paddle.static.nn.switch_case(
                     branch_index=index_2,
                     branch_fns=[(0, fn_1), (4, fn_2), (7, fn_3)])
 
-                exe = fluid.Executor(fluid.CPUPlace())
+                exe = paddle.static.Executor(paddle.CPUPlace())
                 res_1, res_2, res_3 = exe.run(main_program, fetch_list=[out_1, out_2, out_3])
                 print(res_1)  # [[1. 1.]]
                 print(res_2)  # [[2 2] [2 2]]

python/paddle/nn/__init__.py

@@ -41,7 +41,6 @@ from .clip import clip_by_norm  #DEFINE_ALIAS
 from .control_flow import cond  #DEFINE_ALIAS
 # from .control_flow import DynamicRNN        #DEFINE_ALIAS
 # from .control_flow import StaticRNN        #DEFINE_ALIAS
-from .control_flow import switch_case  #DEFINE_ALIAS
 from .control_flow import while_loop  #DEFINE_ALIAS
 # from .control_flow import rnn        #DEFINE_ALIAS
 # from .decode import BeamSearchDecoder        #DEFINE_ALIAS

python/paddle/nn/control_flow.py

@@ -16,13 +16,10 @@
 from ..fluid.layers import cond  #DEFINE_ALIAS
 from ..fluid.layers import while_loop  #DEFINE_ALIAS
 
-from ..fluid.layers import switch_case  #DEFINE_ALIAS
-
 __all__ = [
     'cond',
     #       'DynamicRNN',
     #       'StaticRNN',
-    'switch_case',
     'while_loop',
     #       'rnn'
 ]

python/paddle/static/nn/__init__.py

@@ -35,6 +35,7 @@ __all__ = [
     'prelu',
     'row_conv',
     'spectral_norm',
+    'switch_case',
 ]
 
 from ...fluid.layers import fc  #DEFINE_ALIAS
@@ -58,5 +59,6 @@ from ...fluid.layers import nce  #DEFINE_ALIAS
 from ...fluid.layers import prelu  #DEFINE_ALIAS
 from ...fluid.layers import row_conv  #DEFINE_ALIAS
 from ...fluid.layers import spectral_norm  #DEFINE_ALIAS
+from ...fluid.layers import switch_case  #DEFINE_ALIAS
 
 from ...fluid.input import embedding  #DEFINE_ALIAS