Question data is

"a, b, c, d are stored in separate columns" (7x5 DF)

"a, b, c, d are stored in the same column as part of the string" (7x1 DF)

I can't tell which one is, so there are two answers

When "a, b, c, d are stored in separate columns"

import pandas as pd
import io
data = "" "
A, B, C, D, E
a ,,,,
a, b ,,,
a, b, b ,,
a, b, c ,,
a, b, c, d,
a, a, a, b,
a, d, d, d, a
"" "
df = pd.read_csv (io.StringIO (data)) #, header = None)
ret = df [~ (df == 'b'). any (axis = 1)]
print (ret)
# A B C D E
# 0 a NaN NaN NaN NaN
# 6 a d d d a

"a, b, c, d are stored in the same column as part of the string"

data = "" "
A
a
a b
a b b
a b c
a b c d
a a a b
a d d d a
"" "
df = pd.read_csv (io.StringIO (data))
ret = df [~ df.iloc [:, 0] .str.contains ('b')]
print (ret)
# A
# 0 a
# 6 a d d d a

In any case,

Create Boolian list of whether or not'b'is included in the line

Filter the original data frame using that list

I think it can be achieved