import gi
gi.require_version('Gdk', '3.0')
from gi.repository import Gdk
from gi.repository import Gio
from gi.repository import GLib
from gi.repository import GObject
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk
gi.require_version('Notify', '0.7')
from gi.repository import Notify
蒙圈了

有没有人能给我解释一下？Gdk到底是什么？