code: def tail(self, n=5):
          
          length = _obtain_length(self._length, self._data)
  
          new_index = self.index.tail(n)
          new_data = OrderedDict((column.name, _series_tail(column, new_index, length, n))
                                 for column in self._iter())
  
          return DataFrame(new_data, new_index)
docs: Return DataFrame with last n values per column.
  
          Parameters
          ----------
          n : int
              Number of values.
  
          Returns
          -------
          DataFrame
              DataFrame containing the last n values per column.
  
          Examples
          --------
          >>> df = bl.DataFrame(OrderedDict((('a', np.arange(5, 8)), ('b', np.arange(3)))))
          >>> print(df.tail(2).evaluate())
                 a    b
          ---  ---  ---
            1    6    1
            2    7    2