Question

I want to start a child process and read its stderr, but so far, I can’t read anything at all using subprocess.Popen, even stdout. I’m trying to use subprocess.communicate() to read from stdout and stderr. This is what I do:

import subprocess
p = subprocess.Popen('ls')
s = p.communicate()
print s

This gives me output (None, None). I think the pair is for stdin and stderr. Is that the case? Anyway, how can I read stdout and stderr from a process started with subprocess.Popen?

Answer 1

You need to specify the stdout=subprocess.PIPE and stderr=subprocess.PIPE when you create your Popen object:

  p = subprocess.Popen('ls', stdout=subprocess.PIPE, stderr=subprocess.PIPE)