DOC: updating docstring of Index.shift (pandas-dev#19996)

pandas/core/indexes/base.py

@@ -2211,13 +2211,55 @@ def sortlevel(self, level=None, ascending=True, sort_remaining=None):
         return self.sort_values(return_indexer=True, ascending=ascending)
 
     def shift(self, periods=1, freq=None):
-        """
-        Shift Index containing datetime objects by input number of periods and
-        DateOffset
+        """Shift index by desired number of time frequency increments.
+
+        This method is for shifting the values of datetime-like indexes
+        by a specified time increment a given number of times.
+
+        Parameters
+        ----------
+        periods : int
+            Number of periods (or increments) to shift by,
+            can be positive or negative (default is 1).
+        freq : pandas.DateOffset, pandas.Timedelta or string
+            Frequency increment to shift by (default is None).
+            If None, the index is shifted by its own `freq` attribute.
+            Offset aliases are valid strings, e.g., 'D', 'W', 'M' etc.
 
         Returns
         -------
-        shifted : Index
+        pandas.Index
+            shifted index
+
+        Examples
+        --------
+        Put the first 5 month starts of 2011 into an index.
+
+        >>> month_starts = pd.date_range('1/1/2011', periods=5, freq='MS')
+        >>> month_starts
+        DatetimeIndex(['2011-01-01', '2011-02-01', '2011-03-01', '2011-04-01',
+                       '2011-05-01'],
+                      dtype='datetime64[ns]', freq='MS')
+
+        Shift the index by 10 days.
+
+        >>> month_starts.shift(10, freq='D')
+        DatetimeIndex(['2011-01-11', '2011-02-11', '2011-03-11', '2011-04-11',
+                       '2011-05-11'],
+                      dtype='datetime64[ns]', freq=None)
+
+        The default value of `freq` is the `freq` attribute of the index,
+        which is 'MS' (month start) in this example.
+
+        >>> month_starts.shift(10)
+        DatetimeIndex(['2011-11-01', '2011-12-01', '2012-01-01', '2012-02-01',
+                       '2012-03-01'],
+                      dtype='datetime64[ns]', freq='MS')
+
+        Notes
+        -----
+        This method is only implemented for datetime-like index classes,
+        i.e., DatetimeIndex, PeriodIndex and TimedeltaIndex.
         """
         raise NotImplementedError("Not supported for type %s" %
                                   type(self).__name__)