How do I get sys.stdout to be monitored by GObject.io_add_watch?

code:

        GObject.io_add_watch(os.fdopen(self.builder), GObject.IO_IN, self.write_to_buffer)

I tried to get the stdout stream of my main GTK process via os.fdopen(self.builder), yet it raises the exception:

TypeError: an integer is required

Could you please explain how I have to properly advise GObject.io_add_watch to watch the sys.stdout stream?

Thanks!

Solution

The API will let you pass sys.stdout directly, since it's a file-like object with a fileno() method. It won't work right, though, because you can't read from sys.stdout. If you want to capture all attempts to write to stdout, you can replace it with a pipe:

import gobject
import sys
import os

def ok(stream, condition):
    s = os.fdopen(stream)
    data = s.readline()
    with open("called.txt", "w") as f:
        f.write("got {} ".format(data))
    return False

def do_print():
    print "hey there"
    sys.stdout.flush()

rpipe, wpipe = os.pipe()
wpipe = os.fdopen(wpipe, "w", 0)
sys.stdout = wpipe  # Replace sys.stdout
gobject.io_add_watch(rpipe, gobject.IO_IN, ok)
gobject.idle_add(do_print)
gobject.MainLoop().run()

Contents of "called.txt" after running the script:

got hey there