python的pandas中dataframe索引获取get_loc的用法
官方参考：https://pandas.pydata.org/pandas-docs/stable/generated/pandas.Index.get_loc.html
>>> unique_index = pd.Index(list('abc'))
>>> unique_index.get_loc('b')
1
>>> monotonic_index = pd.Index(list('abbc'))
>>> monotonic_index.get_loc('b')
slice(1, 3, None)
>>> non_monotonic_index = pd.Index(list('abcb'))
>>> non_monotonic_index.get_loc('b')
array([False, True, False, True], dtype=bool)