unique.txt file contains: 2 columns with columns separated by tab. total.txt file contains: 3 columns each column separated by tab. I take each row from unique.txt file and find that in total.txt file. If present then extract entire row from total.txt and save it in new output file. ###Total.txt column a column b column c interaction1 mitochondria_205000_225000 mitochondria_195000_215000 interaction2 mitochondria_345000_365000 mitochondria_335000_355000 interaction3 mitochondria_345000_365000 mitochondria_5000_25000 interaction4 chloroplast_115000_128207 chloroplast_35000_55000 interaction5 chloroplast_115000_128207 chloroplast_15000_35000 interaction15 2_10515000_10535000 2_10505000_10525000 ###Unique.txt column a column b mitochondria_205000_225000 mitochondria_195000_215000 mitochondria_345000_365000 mitochondria_335000_355000 mitochondria_345000_365000 mitochondria_5000_25000 chloroplast_115000_128207 chloroplast_35000_55000 chloroplast_115000_128207 chloroplast_15000_35000 mitochondria_185000_205000 mitochondria_25000_45000 2_16595000_16615000 2_16585000_16605000 4_2785000_2805000 4_2775000_2795000 4_11395000_11415000 4_11385000_11405000 4_2875000_2895000 4_2865000_2885000 4_13745000_13765000 4_13735000_13755000 My program: file=open('total.txt') file2 = open('unique.txt') all_content=file.readlines() all_content2=file2.readlines() store_id_lines = [] ff = open('match.dat', 'w') for i in range(len(all_content)): line=all_content[i].split('\t') seq=line[1]+'\t'+line[2] for j in range(len(all_content2)): if all_content2[j]==seq: ff.write(seq) break Problem: but istide of giving desire output (values of those 1st column that fulfile the if condition). i nead somthing like if jth of unique.txt == ith of total.txt then write ith row of total.txt into new file.