dicto aninhado para df
user_dict = {12: {'Category 1': {'att_1': 1, 'att_2': 'whatever'},
'Category 2': {'att_1': 23, 'att_2': 'another'}},
15: {'Category 1': {'att_1': 10, 'att_2': 'foo'},
'Category 2': {'att_1': 30, 'att_2': 'bar'}}}
pd.DataFrame.from_dict({(i,j): user_dict[i][j]
for i in user_dict.keys()
for j in user_dict[i].keys()},
orient='index')
att_1 att_2
12 Category 1 1 whatever
Category 2 23 another
15 Category 1 10 foo
Category 2 30 bar
Sachin