How to use the vapoursynth.get_output function in VapourSynth

def do_encode(line, cell=None, local_ns=None, stderr=sys.stderr, stdout=sys.stdout, decode_stdout=True, decode_stderr=True, y4m=True):
    if cell is not None:
        cmd = line
        expr = cell
    else:
        try:
            expr, cmd = line.split(" ", 1)
        except ValueError:
            return "No command given"

    clip = retrieve_clip(expr, local_ns)

    if not isinstance(clip, vapoursynth.VideoNode):
        try:
            clip = vapoursynth.get_output(clip)
        except KeyError:
            return "The expression must compute to a VideoNode not '%r'." % clip

    return run_encoder(clip, cmd, stderr=stderr, stdout=stdout, decode_stdout=decode_stdout, decode_stderr=decode_stderr, y4m=y4m)

def format_core(core):
    try:
        return format_video(vs.get_output(0))
    except KeyError:
        return b""

def format_core(core):
    try:
        return video_converter(vs.get_output(0))
    except KeyError:
        return b""

def vpy_source_filter(path):
    import runpy
    runpy.run_path(path, {}, "__vapoursynth__")
    return vapoursynth.get_output(0)

def __getitem__(self, item):
        import vapoursynth
        with find_environment():
            item = vapoursynth.get_output(item)
            if id(item) != self.current_output_ids[item]:
                return None

        return item