How to convert index of a pandas dataframe into a column

How to convert an index of a dataframe into a column?

For example:
gi ptt_loc
0 384444683 593
1 384444684 594
2 384444686 596


to
index1 gi ptt_loc
0 0 384444683 593
1 1 384444684 594
2 2 384444686 596


either:

df['index1'] = df.index

or .reset_index:

df = df.reset_index()

If you have a multi-index frame with 3 levels of index, like:

>>> df
                       val
tick       tag obs        
2016-02-26 C   2    0.0139
2016-02-27 A   2    0.5577
2016-02-28 C   6    0.0303

and you want to convert the 1st (tick) and 3rd (obs) levels in the index into columns, you could do:

>>> df.reset_index(level=['tick', 'obs'])
          tick  obs     val
tag                        
C   2016-02-26    2  0.0139
A   2016-02-27    2  0.5577
C   2016-02-28    6  0.0303

Stack Overflow Q#20461165, score: 1400