["python","pandas","dataframe","multi-index"]
How to simply add a column level to a pandas dataframe

let's say I have a dataframe that looks like this: df = pd.DataFrame({'A': range(5), 'B': range(5)}, index=list('abcde')) df Out[92]: A B a 0 0 b 1 1 c 2 2 d 3 3 e 4 4 Asumming that this dataframe already exist, how can I simply add a level 'C' to the column index so I get this: df Out[92]: A B C C a 0 0 b 1 1 c 2 2 d 3 3 e 4 4 I saw SO anwser like this python/pandas: how to combine two dataframes into one with hierarchical column index? but this concat different dataframe instead of adding a column level to an already existing dataframe.
As suggested by @StevenG himself, a better answer: df.columns = pd.MultiIndex.from_product(df.columns.levels + [['C']]) print(df) # A B # C C # a 0 0 # b 1 1 # c 2 2 # d 3 3 # e 4 4