如何写入Python子进程的stderr？

Question

This question is the same as python subprocess.Popen - write to stderr . But there is no correct answers.

I know this is correct.

import sys
sys.stderr.write('abcd')

Here is the code of subprocess(named input). And I want the child process (input) to print the string written by parent process.

int main(int argc, char* argv[], char* envp[]){
    char buf[5];
    read(2, buf, 4);
    buf[4]=0;
    printf("%s\n", buf);
}

I want to write to a Python subprocess' stderr. However, this is not correct. (Maybe you can correct this or just introduce me another way.)

from subprocess import *
p = Popen(['./input'],stderr=PIPE)
p.stderr.write('abcd')

I got error like this.

IOError: File not open for writing

Thanks for your help.

Answer 1

os.pipe()

Open a pipe to or from command. The return value is an open file object connected to the pipe, which can be read or written depending on whether mode is 'r' (default) or 'w'. The bufsize argument has the same meaning as the corresponding argument to the built-in open() function. The exit status of the command (encoded in the format specified for wait()) is available as the return value of the close() method of the file object, except that when the exit status is zero (termination without errors), None is returned.

Change your Python code to this:

from subprocess import *
import os

r, w = os.pipe()
p = Popen(['./input'],stderr=r, stdout=PIPE)
os.close(r)
os.write(w, b'abcd')
os.close(w)
print(repr(p.communicate()[0]))

You can read Python os.pipe Examples .