Set the O_NONBLOCK flag for a file descriptor. Availability: Unix.

def setblocking(fd, blocking):
    """Set the O_NONBLOCK flag for a file descriptor. Availability: Unix."""
    if not fcntl:
        warnings.warn('setblocking() not supported on Windows')
    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
    if blocking:
        flags |= os.O_NONBLOCK
    else:
        flags &= ~os.O_NONBLOCK
    fcntl.fcntl(fd, fcntl.F_SETFL, flags)