code: def add_prefix(self, prefix):
          
          f = functools.partial('{prefix}{}'.format, prefix=prefix)
  
          mapper = {self._info_axis_name: f}
          return self.rename(**mapper)
docs: Prefix labels with string `prefix`.
  
          For Series, the row labels are prefixed.
          For DataFrame, the column labels are prefixed.
  
          Parameters
          ----------
          prefix : str
              The string to add before each label.
  
          Returns
          -------
          Series or DataFrame
              New Series or DataFrame with updated labels.
  
          See Also
          --------
          Series.add_suffix: Suffix row labels with string `suffix`.
          DataFrame.add_suffix: Suffix column labels with string `suffix`.
  
          Examples
          --------
          >>> s = pd.Series([1, 2, 3, 4])
          >>> s
          0    1
          1    2
          2    3
          3    4
          dtype: int64
  
          >>> s.add_prefix('item_')
          item_0    1
          item_1    2
          item_2    3
          item_3    4
          dtype: int64
  
          >>> df = pd.DataFrame({'A': [1, 2, 3, 4],  'B': [3, 4, 5, 6]})
          >>> df
             A  B
          0  1  3
          1  2  4
          2  3  5
          3  4  6
  
          >>> df.add_prefix('col_')
               col_A  col_B
          0       1       3
          1       2       4
          2       3       5
          3       4       6