The other answers didn't cover the case where you want forked processes to share your new stdout.
To do that:
from os import open, close, dup, O_WRONLY old = dup(1) close(1) open("file", O_WRONLY) # should open on 1 ..... do stuff and then restore close(1) dup(old) # should dup to 1 close(old) # get rid of left overs