pynative add identity primitive and add comment for set_grad

mindspore/nn/cell.py

@@ -853,8 +853,15 @@ class Cell:
         self.add_flags_recursive(**flags)
         return self
 
-    def set_grad(self, mode=True):
-        self.requires_grad = mode
+    def set_grad(self, requires_grad=True):
+        """
+        Sets the cell flag for gradient.
+
+        Args:
+            requires_grad (bool): Specifies if the net need to grad, if it is
+                True, cell will construct backward network in pynative mode. Default: True.
+        """
+        self.requires_grad = requires_grad
         return self
 
     def set_train(self, mode=True):

mindspore/ops/functional.py

@@ -82,6 +82,7 @@ pack = P.Pack()
 partial = P.Partial()
 # depend: mount a node to another node
 depend = P.Depend()
+identity = P.identity()
 
 tuple_setitem = Primitive('tuple_setitem')
 tuple_getitem = Primitive('tuple_getitem')
@@ -135,7 +136,6 @@ broadcast_gradient_args = Primitive('BroadcastGradientArgs')
 dot = Primitive('dot')
 array_reduce = Primitive('array_reduce')
 zeros_like = P.ZerosLike()
-identity = Primitive('identity')
 distribute = Primitive('distribute')
 embed = Primitive('embed')
 ref_to_embed = _grad_ops.RefToEmbed()

mindspore/ops/operations/__init__.py

@@ -83,7 +83,7 @@ from .nn_ops import (LSTM, SGD, Adam, FusedSparseAdam, FusedSparseLazyAdam, Appl
 from . import _quant_ops
 from ._quant_ops import *
 from .other_ops import (Assign, IOU, BoundingBoxDecode, BoundingBoxEncode, PopulationCount,
-                        CheckValid, MakeRefKey, Partial, Depend, CheckBprop, Push, Pull)
+                        CheckValid, MakeRefKey, Partial, Depend, identity, CheckBprop, Push, Pull)
 from ._thor_ops import (CusBatchMatMul, CusCholeskyTrsm, CusFusedAbsMax1, CusImg2Col, CusMatMulCubeDenseLeft,
                         CusMatMulCubeFraczRightMul, CusMatMulCube, CusMatrixCombine, CusTranspose02314,
                         CusMatMulCubeDenseRight,
@@ -266,6 +266,7 @@ __all__ = [
     'MakeRefKey',
     'Partial',
     'Depend',
+    'identity',
     'AvgPool',
     # Back Primitive
     'Equal',

mindspore/ops/operations/other_ops.py

@@ -560,3 +560,21 @@ class Pull(PrimitiveWithInfer):
 
     def infer_dtype(self, key_dtype, weight_dtype):
         return mstype.float32
+
+class identity(Primitive):
+    """
+    Make a identify primitive, used for pynative mode.
+
+    Inputs:
+        - **x** (Any) - identity input value.
+
+    Outputs:
+        The same as input.
+    """
+
+    @prim_attr_register
+    def __init__(self):
+        pass
+
+    def __call__(self, x):
+        return x