Extract rows based on values from text file using Python

Question

I have a list of information in file A that I want to extract according to the numbering in file B. If given the value 4 and 5, all the 4th column in file A with the value 4 and 5 will be extracted. May I know how can I do this using python? can anyone help me? The code below only extract based on index that have value 4.

with open("B.txt", "rt") as f:
    classes = [int(line) for line in f.readlines()]
    with open("A.txt", "rt") as f:
        lines = [line for index, line in enumerate(f.readlines()) if classes[index]== 4]
        lines_all= "".join(lines)

with open("C.txt", "w") as f:
        f.write(lines_all)

A.txt

hg17_ct_ER_ER_1003  36  42  1
hg17_ct_ER_ER_1003  109 129 2
hg17_ct_ER_ER_1003  110 130 2
hg17_ct_ER_ER_1003  129 149 2
hg17_ct_ER_ER_1003  130 150 2
hg17_ct_ER_ER_1003  157 163 3
hg17_ct_ER_ER_1003  157 165 3
hg17_ct_ER_ER_1003  179 185 4
hg17_ct_ER_ER_1003  197 217 5
hg17_ct_ER_ER_1003  220 226 6

B.txt

4
5

Desired output

hg17_ct_ER_ER_1003  179 185 4
hg17_ct_ER_ER_1003  197 217 5

Answer 1

with open("B.txt", "r") as target_file:
    target = [i.strip() for i in target_file]

with open("A.txt", "r") as data_file:
    r = filter(lambda x: x.strip().rsplit(None, 1)[1] in target, data_file)

print "".join(r)

the output:

hg17_ct_ER_ER_1003  179 185 4
hg17_ct_ER_ER_1003  197 217 5

As mentioned by @Padraic, I change the split()[-1] to rsplit(None, 1)[1].

Answer 2

create a set of the lines/numbers from the b file the compare the last element from each row in f1 to the elements in the set:

import  csv    
with open("a.txt") as f, open("b.txt") as f2:
    st = set(line.rstrip() for line in f2)
    r = csv.reader(f,delimiter=" ")
    data = [row for row in r if row[-1] in st]
    print(data)

[['hg17_ct_ER_ER_1003', '179', '185', '4'], ['hg17_ct_ER_ER_1003', '197', '217', '5']]

set delimiter= to whatever it is or don't set it at all if your file is comma separated.

Or:

with open("a.txt") as f, open("b.txt") as f2:
    st = set(line.rstrip() for line in f2)
    data = [line.rstrip() for line in f if line.rsplit(None, 1)[1] in st ]
    print(data)
['hg17_ct_ER_ER_1003 179 185 4', 'hg17_ct_ER_ER_1003 197 217 5']