filtering pandas dataframe using isin function

import pandas as pd
df = pd.DataFrame({'A':[1,2,3], 'B':[4,5,6]})
#Selecting data based on column values
df['A1'] = 1
df['A2'] = 2
df['A3'] = 3
df['A4'] = 4
df['A5'] = 5
df['A6'] = 6
df['A7'] = 7
df['A8'] = 8
#Excluding some of the columns