DOC: Fix errors in pandas.DataFrame.sort_index

pandas/core/frame.py

@@ -4824,6 +4824,9 @@ def sort_index(
         """
         Sort object by labels (along an axis).
 
+        Returns a new DataFrame sorted by label if `inplace` argument is
+        ``False``, otherwise updates the original DataFrame and returns None.
+
         Parameters
         ----------
         axis : {0 or 'index', 1 or 'columns'}, default 0
@@ -4854,8 +4857,37 @@ def sort_index(
 
         Returns
         -------
-        sorted_obj : DataFrame or None
-            DataFrame with sorted index if inplace=False, None otherwise.
+        DataFrame
+            The original DataFrame sorted by the labels.
+
+        See Also
+        --------
+        Series.sort_index : Sort Series by the index.
+        DataFrame.sort_values : Sort DataFrame by the value.
+        Series.sort_values : Sort Series by the value.
+
+        Examples
+        --------
+        >>> df = pd.DataFrame([1, 2, 3, 4, 5], index=[100, 29, 234, 1, 150],
+        ...                   columns=['A'])
+        >>> df.sort_index()
+             A
+        1    4
+        29   2
+        100  1
+        150  5
+        234  3
+
+        By default, it sorts in ascending order, to sort in descending order,
+        use ``ascending=False``
+
+        >>> df.sort_index(ascending=False)
+             A
+        234  3
+        150  5
+        100  1
+        29   2
+        1    4
         """
         # TODO: this can be combined with Series.sort_index impl as
         # almost identical