Nsryjdtyk

I figured out this workaround:

>>> p = subprocess.Popen(['grep','f'],stdout=subprocess.PIPE,stdin=subprocess.PIPE)

>>> p.stdin.write(b'onentwonthreenfournfivensixn') #expects a bytes type object

>>> p.communicate()[0]

'fournfiven'

>>> p.stdin.close()

Is there a better one?

I'm a bit surprised nobody suggested creating a pipe, which is in my opinion the far simplest way to pass a string to stdin of a subprocess:

read, write = os.pipe()

os.write(write, "stdin input here")

os.close(write)



subprocess.check_call(['your-command'], stdin=read)

There's a beatiful solution if you're using Python 3.4 or better. Use the input argument instead of the stdin argument, which accepts a bytes argument:

output = subprocess.check_output(

    ["sed", "s/foo/bar/"],

    input=b"foo",

)

I am using python3 and found out that you need to encode your string before you can pass it into stdin:

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=PIPE)

out, err = p.communicate(input='onentwonthreenfournfivensixn'.encode())

print(out)

"Apparently a cStringIO.StringIO object doesn't quack close enough to a file duck to suit subprocess.Popen"

:-)

I'm afraid not. The pipe is a low-level OS concept, so it absolutely requires a file object that is represented by an OS-level file descriptor. Your workaround is the right one.

from subprocess import Popen, PIPE

from tempfile import SpooledTemporaryFile as tempfile

f = tempfile()

f.write('onentwonthreenfournfivensixn')

f.seek(0)

print Popen(['/bin/grep','f'],stdout=PIPE,stdin=f).stdout.read()

f.close()

"""

Ex: Dialog (2-way) with a Popen()

"""



p = subprocess.Popen('Your Command Here',

                 stdout=subprocess.PIPE,

                 stderr=subprocess.STDOUT,

                 stdin=PIPE,

                 shell=True,

                 bufsize=0)

p.stdin.write('STARTn')

out = p.stdout.readline()

while out:

  line = out

  line = line.rstrip("n")



  if "WHATEVER1" in line:

      pr = 1

      p.stdin.write('DO 1n')

      out = p.stdout.readline()

      continue



  if "WHATEVER2" in line:

      pr = 2

      p.stdin.write('DO 2n')

      out = p.stdout.readline()

      continue

"""

..........

"""



out = p.stdout.readline()



p.wait()

Beware that Popen.communicate(input=s)may give you trouble ifsis too big, because apparently the parent process will buffer it before forking the child subprocess, meaning it needs "twice as much" used memory at that point (at least according to the "under the hood" explanation and linked documentation found here). In my particular case,swas a generator that was first fully expanded and only then written tostdin so the parent process was huge right before the child was spawned,
and no memory was left to fork it:

File "/opt/local/stow/python-2.7.2/lib/python2.7/subprocess.py", line 1130, in _execute_child
self.pid = os.fork()
OSError: [Errno 12] Cannot allocate memory

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)    

p.stdin.write('onen')

time.sleep(0.5)

p.stdin.write('twon')

time.sleep(0.5)

p.stdin.write('threen')

time.sleep(0.5)

testresult = p.communicate()[0]

time.sleep(0.5)

print(testresult)