Pandas Multi Index From existing index string

Question

I got a Data Frame like This:

 df = pd.DataFrame([[1,2,3,4,5,6], [7,8,9,10,11,12]],columns=["a123X","a123Y","a123Z","b123X", "b123Y", "b123Z"])
   a123X  a123Y  a123Z  b123X  b123Y  b123Z
0      1      2      3      4      5      6
1      7      8      9     10     11     12

and I want to make the X Y Z a multi index. Currently I use a work around like that:

df.columns = (df.columns.str[:-1] + "_" + df.columns.str[-1]).str.split("_", expand=True)
  a123       b123        
     X  Y  Z    X   Y   Z
0    1  2  3    4   5   6
1    7  8  9   10  11  12

Is there any way to make this easier it will always be the last letter which will be the second level in the index.

Answer 1

Assign nested lists back:

df.columns = [df.columns.str[:-1],  df.columns.str[-1]]
print (df)

  a123       b123        
     X  Y  Z    X   Y   Z
0    1  2  3    4   5   6
1    7  8  9   10  11  12