Python - How do I pass a string into subprocess.Popen (using the stdin argument)?

问题

If I do the following:

import subprocess
from cStringIO import StringIO
subprocess.Popen([\'grep\',\'f\'],stdout=subprocess.PIPE,stdin=StringIO(\'one\\ntwo\\nthree\\nfour\\nfive\\nsix\\n\')).communicate()[0]

I get:

Traceback (most recent call last):
  File \"<stdin>\", line 1, in ?
  File \"/build/toolchain/mac32/python-2.4.3/lib/python2.4/subprocess.py\", line 533, in __init__
    (p2cread, p2cwrite,
  File \"/build/toolchain/mac32/python-2.4.3/lib/python2.4/subprocess.py\", line 830, in _get_handles
    p2cread = stdin.fileno()
AttributeError: \'cStringIO.StringI\' object has no attribute \'fileno\'

Apparently a cStringIO.StringIO object doesn\'t quack close enough to a file duck to suit subprocess.Popen. How do I work around this?

回答1:

Popen.communicate() documentation:

Note that if you want to send data to the process’s stdin, you need to create the Popen object with stdin=PIPE. Similarly, to get anything other than None in the result tuple, you need to give stdout=PIPE and/or stderr=PIPE too.

Replacing os.popen*

    pipe = os.popen(cmd, 'w', bufsize)
    # ==>
    pipe = Popen(cmd, shell=True, bufsize=bufsize, stdin=PIPE).stdin

Warning Use communicate() rather than stdin.write(), stdout.read() or stderr.read() to avoid deadlocks due to any of the other OS pipe buffers filling up and blocking the child process.

So your example could be written as follows:

from subprocess import Popen, PIPE, STDOUT

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)    
grep_stdout = p.communicate(input=b'one\ntwo\nthree\nfour\nfive\nsix\n')[0]
print(grep_stdout.decode())
# -> four
# -> five
# ->

On the current Python 3 version, you could use subprocess.run, to pass input as a string to an external command and get its exit status, and its output as a string back in one call:

#!/usr/bin/env python3
from subprocess import run, PIPE

p = run(['grep', 'f'], stdout=PIPE,
        input='one\ntwo\nthree\nfour\nfive\nsix\n', encoding='ascii')
print(p.returncode)
# -> 0
print(p.stdout)
# -> four
# -> five
# ->

回答2:

I figured out this workaround:

>>> p = subprocess.Popen(['grep','f'],stdout=subprocess.PIPE,stdin=subprocess.PIPE)
>>> p.stdin.write(b'one\ntwo\nthree\nfour\nfive\nsix\n') #expects a bytes type object
>>> p.communicate()[0]
'four\nfive\n'
>>> p.stdin.close()

Is there a better one?

回答3:

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)

回答4:

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",
)

回答5:

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='one\ntwo\nthree\nfour\nfive\nsix\n'.encode())
print(out)

回答6:

"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.

回答7:

from subprocess import Popen, PIPE
from tempfile import SpooledTemporaryFile as tempfile
f = tempfile()
f.write('one\ntwo\nthree\nfour\nfive\nsix\n')
f.seek(0)
print Popen(['/bin/grep','f'],stdout=PIPE,stdin=f).stdout.read()
f.close()

回答8:

"""
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('START\n')
out = p.stdout.readline()
while out:
  line = out
  line = line.rstrip("\n")

  if "WHATEVER1" in line:
      pr = 1
      p.stdin.write('DO 1\n')
      out = p.stdout.readline()
      continue

  if "WHATEVER2" in line:
      pr = 2
      p.stdin.write('DO 2\n')
      out = p.stdout.readline()
      continue
"""
..........
"""

out = p.stdout.readline()

p.wait()

回答9:

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

回答10:

p = Popen(['grep', 'f'], stdout=PIPE, stdin=PIPE, stderr=STDOUT)    
p.stdin.write('one\n')
time.sleep(0.5)
p.stdin.write('two\n')
time.sleep(0.5)
p.stdin.write('three\n')
time.sleep(0.5)
testresult = p.communicate()[0]
time.sleep(0.5)
print(testresult)

来源：https://stackoverflow.com/questions/163542/python-how-do-i-pass-a-string-into-subprocess-popen-using-the-stdin-argument

标签

python

subprocess

stdin