Python redirect stdin/stdout with execv

Question

I'm using python to os.fork a child progress, and use os.execv to execute another program in the child progress. How can I redirect I/O in the child program. I tried this but failed.

import sys, os pid = os.fork() if pid is 0: sys.stdin = open('./test.in') os.execv('/usr/bin/python', ['python', './test.py'])

While test.py is:

import sys print(sys.stdin) a = input() print(a)

@JoachimPileborg : subprocess is good but not what I want, since I want to limit resource in the child process. — Bin Wang
– Bin Wang, Commented Jan 24, 2013 at 6:37
Looks like this is what you want: stackoverflow.com/a/8500169/10601 — perimosocordiae
– perimosocordiae, Commented Jan 24, 2013 at 6:50
if pid is 0 is wrong. You must use if pid == 0. Your may happen to work in all versions of CPython (so far), but the language does not in any way guarantee that the 0 returned by os.fork() and the 0 against which you are comparing are the same 0 object. In future CPython versions or in other Python implementations like PyPy, they might very well not be the same 0. — Celada
– Celada, Commented Jan 24, 2013 at 14:01

mib0163 · Accepted Answer · 2015-07-13 20:48:31Z

After os.fork() try this to redirect stdin and stderr:

import os STDIN_FILENO = 0 STDOUT_FILENO = 1 STDERR_FILENO = 2 # redirect stdout new_stdout = os.open(stdout_file, os.O_WRONLY|os.O_CREAT|os.O_TRUNC) os.dup2(new_stdout, STDOUT_FILENO) # redirect stderr new_stderr = os.open(stderr_file, os.O_WRONLY|os.O_CREAT|os.O_TRUNC) os.dup2(new_stderr, STDERR_FILENO)

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