from subprocess import Popen, PIPE
import tempfile

with tempfile.TemporaryFile() as tempf:
    proc = Popen(['echo', 'a', 'b'], stdout=tempf)
    proc.wait()
    tempf.seek(0)
    print tempf.read()

    proc = Popen(['ifconfig'], stdout=tempf)
    proc.wait()
    tempf.seek(0)
    print tempf.read()、''