python 重命名轴索引的方法

import numpy as npfrom pandas import Series, DataFrame###重命名轴索引data = DataFrame(np.arange(12).reshape((3, 4)),     index=['Ohio', 'Colorado', 'New York'],     columns=['one', 'two', 'three', 'four']) print( data.index.map(str.upper) ) #['OHIO' 'COLORADO' 'NEW YORK'] data.index = data.index.map(str.upper)print( data )'''   one two three fourOHIO  0 1  2  3COLORADO 4 5  6  7NEW YORK 8 9  10 11''' data_2 = data.rename(index=str.title, columns=str.upper)print( data_2 )'''   ONE TWO THREE FOUROhio  0 1  2  3Colorado 4 5  6  7New York 8 9  10 11'''data_3 = data.rename(index={'OHIO': 'INDIANA'},   columns={'three': 'peekaboo'})print( data_3 )'''   one two peekaboo fourINDIANA  0 1   2  3COLORADO 4 5   6  7NEW YORK 8 9  10 11''' # 总是返回DataFrame的引用_ = data.rename(index={'OHIO': 'INDIANA'}, inplace=True)print( _ ) # None