def concat_iter(file1, file2, output):
    with open(output, 'w', 1024) as fo:
        with open(file1, 'r') as f1:
            with open(file2, 'r') as f2:
                fo.write(''.join('{}\t{}'.format(l1, l2) for l1, l2 in zip
                    (f1.readlines(1024), f2.readlines(1024))))
Fastest way to concatenate multiple files column wise - Python