Update while loop (#34229)

* update readme test=document_fix

* update while loop docs test=document_fix

Author: TCChenlong

python/paddle/fluid/layers/control_flow.py

@@ -1133,45 +1133,29 @@ def while_loop(cond, body, loop_vars, is_test=False, name=None):
             refer to :ref:`api_guide_Name`. Default is None.
 
     Returns:
-        A list or tuple of tensors or LoDTensorArrays which returned by ``body`` .
-    
-    Returen type:
-        list(Variable)|tuple(Variable).
-
-    Raises:
-        TypeError: If the type of ``cond`` is not callable.
-        TypeError: If the type of ``body`` is not callable.
-        TypeError: If the type of ``loop_vars`` is not list or tuple.
-        TypeError: If the type of ``cond`` returns is not Variable.
-        TypeError: If the type of ``cond`` returns is not a boolean variable.
-        TypeError: If the shape of ``cond`` returns is not equals 1.
-        ValueError: If the ``var_loops`` is empty.
-        ValueError: If the length or type of ``body`` returns is not same as ``loop_vars``.
+        A list or tuple of Tensors or LoDTensorArrays which returned by ``body`` .
 
     Examples:
         .. code-block:: python
 
-            import paddle.fluid as fluid
-            import paddle.fluid.layers as layers
             import paddle
             paddle.enable_static()
 
-
             def cond(i, ten):
                 return i < ten
 
             def body(i, ten):
                 i = i + 1
                 return [i, ten]
 
-            main_program = fluid.default_main_program()
-            startup_program = fluid.default_startup_program()
-            with fluid.program_guard(main_program, startup_program):
-                i = layers.fill_constant(shape=[1], dtype='int64', value=0)     # loop counter
-                ten = layers.fill_constant(shape=[1], dtype='int64', value=10)  # loop length
-                i, ten = layers.while_loop(cond, body, [i, ten])
+            main_program = paddle.static.default_main_program()
+            startup_program = paddle.static.default_startup_program()
+            with paddle.static.program_guard(main_program, startup_program):
+                i = paddle.full(shape=[1], fill_value=0, dtype='int64')     # loop counter
+                ten = paddle.full(shape=[1], fill_value=10, dtype='int64')  # loop length
+                i, ten = paddle.static.nn.while_loop(cond, body, [i, ten])
                 
-                exe = fluid.Executor(fluid.CPUPlace())
+                exe = paddle.static.Executor(paddle.CPUPlace())
                 res = exe.run(main_program, feed={}, fetch_list=[i])
                 print(res) # [array([10])]
     """