1In [1]: df = pd.read_csv('foo.csv', index_col=0)
2
3In [2]: df
4Out[2]:
5 A B C
60 1 2 3
71 4 5 6
8
9In [3]: df + 6
10Out[3]:
11 A B C
120 7 8 9
131 10 11 12
14
15In [4]: with open('foo.csv', 'a') as f:
16 (df + 6).to_csv(f, header=False)