fix api for tensor.item and tensor.itemset

mindspore/common/tensor.py

@@ -344,19 +344,67 @@ class Tensor(Tensor_):
         """
         Getitem from the Tensor with the index.
 
+        Note:
+            Tensor.item returns a Tensor scalar instead of a Python scalar.
+
         Args:
             index (Union[None, int, tuple(int)]): The index in Tensor. Default: None.
 
         Returns:
-            Tensor getitem by index whose dtype is int or tuple with int. If index is None,
-            the `item` API can only convert an array of size 1 to a Python scalar.
+            A Tensor scalar, dtype is the same with the original Tensor.
+
+        Raises:
+            ValueError: If the length of the `index` is not euqal to self.ndim.
+
+        Supported Platforms:
+            ``Ascend`` ``GPU``
+
+        Examples:
+            >>> import numpy as np
+            >>> from mindspore import Tensor
+            >>> x = Tensor(np.array([[1,2,3],[4,5,6]], dtype=np.float32))
+            >>> x = x.item((0,1))
+            >>> print(x)
+            2.0
 
         """
         output = tensor_operator_registry.get('item')(self, index)
         return output
 
     def itemset(self, *args):
-        """Setitem from the Tensor with the index."""
+        """
+        Insert scalar into a tensor (scalar is cast to tensor’s dtype, if possible).
+
+        There must be at least 1 argument, and define the last argument as item.
+        Then, tensor.itemset(*args) is equivalent to :math:`tensor[args] = item`.
+
+        Args:
+            args (Union[(Number), (int/tuple(int), Number)]): The arguments that
+                specify the index and value. If `args` contain one argument (a scalar),
+                it is only used in case tensor is of size 1. If `args` contain two
+                arguments, the last argument is the value to be set and must be a
+                scalar, the first argument specifies a single tensor element location.
+                It is either an int or a tuple.
+
+        Returns:
+            A new Tensor, with value set by :math:`tensor[args] = item`.
+
+        Raises:
+            ValueError: If the length of the first argument is not euqal to self.ndim.
+            IndexError: If only one argument is provided, and the original Tensor is not scalar.
+
+        Supported Platforms:
+            ``Ascend`` ``GPU``
+
+        Examples:
+            >>> import numpy as np
+            >>> from mindspore import Tensor
+            >>> x = Tensor(np.array([[1,2,3],[4,5,6]], dtype=np.float32))
+            >>> x = x.itemset((0,1), 4)
+            >>> print(x)
+            [[1. 4. 3.]
+            [4. 5. 6.]]
+        """
         output = tensor_operator_registry.get('itemset')(self, *args)
         return output
 
@@ -1012,7 +1060,6 @@ class Tensor(Tensor_):
 
         Raises:
             TypeError: If input arguments have types not specified above.
-            ValueError: If `shape` has entries < 0.
 
         Supported Platforms:
             ``Ascend`` ``GPU`` ``CPU``