如何在pygtk中将笔记本栏在左侧对齐？

import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk

window = Gtk.Window()
window.connect("destroy", Gtk.main_quit)

notebook = Gtk.Notebook()
notebook.set_tab_pos(Gtk.PositionType.LEFT)

# 添加页面到笔记本中
label1 = Gtk.Label("Page 1")
notebook.append_page(label1, Gtk.Label("Tab 1"))

label2 = Gtk.Label("Page 2")
notebook.append_page(label2, Gtk.Label("Tab 2"))

window.add(notebook)
window.show_all()

Gtk.main()