Add new columns to DataFrame from the value of one column

Use str.get_dummies with cast to bool by astype and add column B by join:

df1 = df['A'].str.get_dummies(',').astype(bool).join(df['B'])
print (df1)
       a     b     c      f  B
0   True  True  True  False  3
1  False  True  True   True  4

More general solution with pop for extract column A:

df = pd.DataFrame({'A':['a,b,c','b,c,f'], 'B':[3,4], 'C':[7,3]})
print (df)
       A  B  C
0  a,b,c  3  7
1  b,c,f  4  3

df1 = df.pop('A').str.get_dummies(',').astype(bool).join(df)
print (df1)
       a     b     c      f  B  C
0   True  True  True  False  3  7
1  False  True  True   True  4  3