GTK REVEALER PROBLEM SC

from gi.repository import Gtk
from gi.repository import Gdk

def revealer_child(button):
    if revealer.get_reveal_child():
        revealer.set_reveal_child(False)
        revealer.hide()
    else:
        revealer.set_reveal_child(True)
        revealer.show()

window = Gtk.Window()
window.set_size_request(Gdk.Screen.get_default().get_width(),20)
window.connect('destroy',Gtk.main_quit)
window.set_size_request(
    Gdk.Screen.get_default().get_width(),
    20)

grid = Gtk.Grid()
window.add(grid)

revealer = Gtk.Revealer()
revealer.set_reveal_child(False)
grid.attach(revealer,0,1,1,1)

notebook = Gtk.Notebook()
for i in range(10):
    box = Gtk.Box()
    box.set_size_request(
        Gdk.Screen.get_default().get_width(),
        Gdk.Screen.get_default().get_height())

    container = Gtk.FlowBox()
    container.set_valign(Gtk.Align.START)
    container.set_max_children_per_line(30)
    container.set_selection_mode(Gtk.SelectionMode.NONE)

    for j in range(10):
        button = Gtk.Button("%d" % i)
        container.add(button)

    box.add(container)
    notebook.append_page(box,Gtk.Label("Label"))

revealer.add(notebook)

button = Gtk.Button("Revealer")
button.connect("clicked",revealer_child)
grid.attach(button,0,0,1,1)

window.show_all()

Gtk.main()