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

A solution which adds a name to the new level and is easier on the eyes than other answers already presented:

df['newlevel'] = 'C'
df = df.set_index('newlevel', append=True).unstack('newlevel')

print(df)
#           A  B
# newlevel  C  C
# a         0  0
# b         1  1
# c         2  2
# d         3  3
# e         4  4