buffering demo

demo.py

#!/usr/bin/env python3

import difflib
import subprocess
import sys

qty = 1000000

seq = subprocess.check_output(
    ('seq', str(qty))).decode('utf-8')
seqjs = subprocess.check_output(
    ('nodejs', 'seq.js', str(qty))).decode('utf-8')

diff = difflib.unified_diff(seq.splitlines(keepends=True),
                            seqjs.splitlines(keepends=True),
                            fromfile='seq', tofile='seqjs')
sys.stdout.writelines(diff)

seq.js

'use strict';

var end = parseInt(process.argv[2]);
var output = ''

for (var i=1; i <= end; i++) {
  output += i + '\n';
}
console.log(output.slice(0, -1));