stream - How to read the first byte of a subprocess's stdout and then discard the rest in Python?

Question

I'd like to read the first byte of a subprocess' stdout to know that it has started running. After that I'd like to discard all further output, so that I don't have to worry about the buffer.

What is the best way to do this?

Clarification: I'd like the subprocess to continue running alongside my program, I don't want to wait for it to terminate or anything like that. Ideally there would be some simple way to do this, without resorting to threading, forking or multiprocessing.

If I ignore the output stream, or .close() it, it causes errors if it is sent more data than it can fit in its buffer.

Answer 1

If you're using Python 3.3+, you can use the DEVNULL special value for stdout and stderr to discard subprocess output.

from subprocess import Popen, DEVNULL

process = Popen(["mycmd", "myarg"], stdout=DEVNULL, stderr=DEVNULL)

Or if you're using Python 2.4+, you can simulate this with:

import os
from subprocess import Popen

DEVNULL = open(os.devnull, 'wb')
process = Popen(["mycmd", "myarg"], stdout=DEVNULL, stderr=DEVNULL)

However this doesn't give you the opportunity to read the first byte of stdout.