How to simply add a column level to a pandas dataframe

Question

let say I have a dataframe that looks like this:

df = pd.DataFrame(index=list(\'abcde\'), data={\'A\': range(5), \'B\': range(5)})
 df
Out[92]: 
   A  B
a  0         


        

Answer 1

option 1
set_index and T

df.T.set_index(np.repeat('C', df.shape[1]), append=True).T

option 2
pd.concat, keys, and swaplevel

pd.concat([df], axis=1, keys=['C']).swaplevel(0, 1, 1)