How to read stdout and stderr and save it all at once with subprocess Popen?

Question

I have seen several questions around this topic already but none has worked for me. What I need is to get hold of the complete stdout and stderr of a subprocess.Popen([...],stdout=subprocess.PIPE) and write it all at once to a file, for example:

import tempfile
import subprocess

stattmpfile = tempfile.NamedTemporaryFile(suffix=".log",prefix="status",delete=False)
proc = subprocess.Popen([mycommand, myparams], stdout=subprocess.PIPE)
while proc.poll() is None:
    output = proc.stdout.readline()
    statusfile.write(output)
output = proc.communicate()[0]
statusfile.write(output)
statusfile.close()

In this example I only get the first line of the standard output and nothing else.

Answer 1

To save both stdout and stderr of a subprocess to a file:

import subprocess

with open('filename', 'wb', 0) as file:
    subprocess.check_call(cmd, stdout=file, stderr=subprocess.STDOUT)