import pandas as pd

index = pd.MultiIndex.from_arrays([['foo', 'foo', 'bar', 'bar'], ['one', 'two', 'one', 'two']], names=['first', 'second'])

df = pd.DataFrame({'A': [1, 2, 3, 4], 'B': [5, 6, 7, 8], 'C': [9, 10, 11, 12]}, index=index)

print(df)

             A  B   C
first second         
foo   one    1  5   9
      two    2  6  10
bar   one    3  7  11
      two    4  8  12

index = pd.MultiIndex.from_tuples([('foo', 'one'), ('foo', 'two'), ('bar', 'one'), ('bar', 'two')], names=['first', 'second'])

grouped = df.groupby('first').sum()

print(grouped)

       A   B   C
first          
bar    7  15  23
foo    3  11  19

grouped = df.groupby('second').sum()

print(grouped)

        A   B   C
second          
one     4  12  20
two     6  14  22