>>> stubnames = ['group1', 'group2']
>>> i = 'Test'
>>> j = 'a-b-Label'
>>> suffix = '.+'
>>> sep = '_'
>>>
>>> stackme
   group1_a1  group1_b2   Test  group2_a1  group2_b2
0       0.45        0.3  Test1          2          6
1       0.03        1.2  Test2          9          7
2       0.70        4.2  Test3          4          2
>>>
>>> pd.wide_to_long(stackme, stubnames=stubnames, i=i, j=j, sep='_', suffix=suffix)
                 group1  group2
Test  a-b-Label
Test1 a1           0.45       2
Test2 a1           0.03       9
Test3 a1           0.70       4
Test1 b2           0.30       6
Test2 b2           1.20       7
Test3 b2           4.20       2