Python, GTK+3 and Glade - connect_signals() not working

Question

I'm trying to write a GUI using Python, GTK+3 and Glade. Following the tutorial, I produced some code. The Problem is, it seems, that the connect_signals() doesn't work, so clicks on buttons don't have any effect.

python:

from gi.repository import Gtk

class Handler:
    def onDeleteWindow(self, *args):
        Gtk.main_quit(*args)

    def onButtonPressed(self, button):
        print("Hello World!")

builder = Gtk.Builder()
builder.add_from_file("gui.glade")

builder.connect_signals(Handler())

window = builder.get_object("window1")
window.show_all()

Gtk.main()

glade:

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- interface-requires gtk+ 3.0 -->
  <object class="GtkWindow" id="window1">
    <property name="can_focus">False</property>
    <child>
      <object class="GtkBox" id="box1">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="orientation">vertical</property>
        <property name="spacing">4</property>
        <child>
                <object class="GtkButton" id="button1">
                <property name="label" translatable="yes">Install</property>
                <property name="use_action_appearance">False</property>
                <property name="visible">True</property>
                <property name="can_focus">True</property>
                <property name="receives_default">True</property>
                <property name="use_action_appearance">False</property>
              </object>
        </child>
      </object>
    </child>
  </object>
</interface>

Answer 1

You have missed out the signal names in the gui.glade file : See the two tags called signal below.

Reference : http://python-gtk-3-tutorial.readthedocs.org/en/latest/builder.html

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- interface-requires gtk+ 3.0 -->
  <object class="GtkWindow" id="window1">
    <property name="can_focus">False</property>
    <signal name="delete-event" handler="onDeleteWindow" swapped="no"/>
    <child>
      <object class="GtkBox" id="box1">
        <property name="visible">True</property>
        <property name="can_focus">False</property>
        <property name="orientation">vertical</property>
        <property name="spacing">4</property>
        <child>
                <object class="GtkButton" id="button1">
                <property name="label" translatable="yes">Install</property>
                <property name="use_action_appearance">False</property>
                <property name="visible">True</property>
                <property name="can_focus">True</property>
                <property name="receives_default">True</property>
                <property name="use_action_appearance">False</property>
                <signal name="pressed" handler="onButtonPressed" swapped="no"/>
              </object>
        </child>
      </object>
    </child>
  </object>
</interface>