Demonstration of the limitation of Python's subprocess.PIPE

pipetest.py

from subprocess import Popen, PIPE
import argparse, time

def execute(n):
  p = Popen(['python', 'test.py', '-n', str(n)], stdin=PIPE, stdout=PIPE, stderr=PIPE)
  p.wait()
  return p.stdout.read().splitlines()

def execute_long(n):
  with open('query.txt','w') as stdout:
    p = Popen(['python', 'test.py', '-n', str(n)], stdin=PIPE, stdout=stdout, stderr=PIPE)
    p.wait()
  with open('query.txt','r') as stdout:
    return stdout.read().splitlines()

if __name__ == "__main__":
  parser = argparse.ArgumentParser()
  parser.add_argument('-n', type=int)
  args = parser.parse_args()
  if args.n is not None:
    print '0'*args.n
  else:
    for n in [10,100,1000,10000,12000,16000,32000,64000,128000]:
      t0 = time.clock()
      execute_long(n)
      print n, time.clock() - t0