df = pd.DataFrame({'col1':[0,1,2], 'col2':[0,1,2], 'col3':[0,1,2]})
df
col1 col2 col3
0 0 0 0
1 1 1 1
2 2 2 2
df['col1'], df['col2'], df['col3'] = zip(*df.apply(lambda r: (1, 2, 3), axis=1))
df
col1 col2 col3
0 1 2 3
1 1 2 3
2 1 2 3