理解dataframe.swaplevel(1,0).sort_index()

• DataFrame.swaplevel(i=-2,j=-1,axis=0)

  Swap level i and j in a MultiIndex on a particular axis.

  i,j : int or str, Levels of the indices to be swapped.

  axis : {0 or ‘index’, 1 or ‘columns’}, default 0. The axis to swap levels on .

• DataFrame.sort_index(axis=0, level=None, ascending=True, inplace=False, kind=‘quicksort’, na_position=‘last’, sort_remaining=True, ignore_index=False, key=None)

  Sort object by labels (along an axis)