子进程checkoutput错误

Question

I am trying to check the usage of check_output using he below script and running into compilation error,where am I going wrong?

import os
import subprocess
from subprocess import check_output

#result = subprocess.check_output(['your_program.exe', 'arg1', 'arg2'])
SCRIPT_ROOT=subprocess.check_output(["pwd","shell=True"])
print SCRIPT_ROOT

def main ():
    pass

if __name__ == '__main__':
    main()

Traceback (most recent call last):
  File "test.py", line 3, in <module>
    from subprocess import check_output
ImportError: cannot import name check_output

Answer 1

check_output has been introduced in Python 2.7. If you're using an earlier version of python, it's just not there.

Alternative is to use Popen .

output = subprocess.Popen(['pwd'], stdout=subprocess.PIPE).communicate()[0]

Proof of this can be found here .

New function: the subprocess module's check_output() runs a command with a specified set of arguments and returns the command's output as a string when the command runs without error, or raises a CalledProcessError exception otherwise.

Demo of the substitute.

import subprocess
cmd = subprocess.Popen(['pwd'], stdout=subprocess.PIPE)
output = cmd.communicate()[0]
print cmd.returncode
print output

Output

> python p.py
/Users/vlazarenko/tests

The only real difference is that Popen won't throw an exception when command returns a non-zero code.

Answer 2

There is no check_output in 2.6. But if you look at the 2.7 source , it's trivial.

In fact, a common way to deal with this is:

import subprocess
try:
    check_output = subprocess.check_output
except AttributeError:
    def check_output(*popenargs, **kwargs):
        # lines 537-545 copied and pasted from 2.7 source

This does of course require that your code be PSFL-compatible (which it almost certainly is, but if it matters, I wouldn't take legal advice from a random guy on SO).

Another option is to use subprocess32 , a backport of the 3.2.3 subprocess module to Python 2.4+, which gives you not only the new 2.7 features and fixes, but a bunch of newer ones. (Personally, whenever I'm writing 2/3 code, I end up writing with subprocess.Popen… and have to either change it to with contextlib.closing(subprocess.Popen… or with subprocess32.Popen …)