import os, subprocess, time

os_filename = "tmp_os"
sub_filename = "tmp_subprocess"

def write_file(filename): # write out a reasonably big file
   fh = file(filename, 'w')
   for i in xrange(100000):
       print >>fh, i
   fh.close()

write_file(os_filename)
write_file(sub_filename)

start = time.time()
read_handle = os.popen('cat %s' % os_filename)
a = [i for i in read_handle]
print "time with os.popen : ", time.time() - start

start = time.time()
read_handle = subprocess.Popen(['cat', sub_filename], stdout=subprocess.PIPE).stdout
a = [i for i in read_handle]
print "time with subprocess.Popen : ", time.time() - start

os.unlink(os_filename)
os.unlink(sub_filename)