!21329 add print for example

Merge pull request !21329 from lianliguang/code_docs_primitive

mindspore/ops/primitive.py

@@ -631,14 +631,14 @@ def constexpr(fn=None, get_instance=True, name=None):
         >>> def tuple_len(x):
         ...     return len(x)
         ...
-        >>> tuple_len(a)
+        >>> print(tuple_len(a))
         2
         >>> # make an operator class to calculate tuple len
         >>> @constexpr(get_instance=False, name="TupleLen")
         >>> def tuple_len_class(x):
         ...     return len(x)
         ...
-        >>> tuple_len_class()(a)
+        >>> print(tuple_len_class()(a))
         2
     """