code: def swaplevel(self, i=-2, j=-1, axis=0):
          
          result = self.copy()
  
          axis = self._get_axis_number(axis)
          if axis == 0:
              result.index = result.index.swaplevel(i, j)
          else:
              result.columns = result.columns.swaplevel(i, j)
          return result
docs: Swap levels i and j in a MultiIndex on a particular axis.
  
          Parameters
          ----------
          i, j : int, string (can be mixed)
              Level of index to be swapped. Can pass level name as string.
  
          Returns
          -------
          DataFrame
  
          .. versionchanged:: 0.18.1
  
             The indexes ``i`` and ``j`` are now optional, and default to
             the two innermost levels of the index.