!12118 support switch layer for pynative

From: @chujinjin
Reviewed-by: @zhoufeng54,@kisnwang
Signed-off-by: @kisnwang

mindspore/common/tensor.py

@@ -161,6 +161,20 @@ class Tensor(Tensor_):
             return bool(data[0])
         raise ValueError("The truth value of an array with several elements is ambiguous.")
 
+    def __index__(self):
+        data = self.asnumpy()
+        if not (data.dtype == "int8"
+                or data.dtype == "int16"
+                or data.dtype == "int32"
+                or data.dtype == "int64"
+                or data.dtype == "bool"):
+            raise ValueError("Only integer tensors of a single element can be converted to an index.")
+        if data.shape == ():
+            return int(data)
+        if data.shape == (1,):
+            return int(data[0])
+        raise ValueError("Only integer tensors of a single element can be converted to an index.")
+
     def __pos__(self):
         return self