os.py 文件源码

def nb_read(fd, n):
        """Read up to `n` bytes from file descriptor `fd`. Return a string
        containing the bytes read. If end-of-file is reached, an empty string
        is returned.

        The descriptor must be in non-blocking mode.
        """
        hub, event = None, None
        while True:
            try:
                return _read(fd, n)
            except OSError, e:
                if e.errno not in ignored_errors:
                    raise
                sys.exc_clear()
            if hub is None:
                hub = get_hub()
                event = hub.loop.io(fd, 1)
            hub.wait(event)