I found that:

Handler “button_1click” should be “button1_click”

The file “test.py” should read the following:

#!/usr/bin/python
# -*- coding: utf-8 -*-

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

from gi.repository import Gtk
   
class Handler:
    def button1_clicked(self, button):
     print "Hello World!"

builder = Gtk.Builder()
builder.add_from_file("myprogram.glade")
builder.connect_signals(Handler())

ournewbutton = builder.get_object("button1")
ournewbutton.set_label("Hello, World!")

window = builder.get_object("window1")

window.connect("delete-event", Gtk.main_quit)
window.show_all()
Gtk.main()

I become fed up with Windows 10, which has basically ruined my HP Pavilion dv7 (the Windows 7 it originally came with ran far better), so I bought a second hand MacBook Pro, which I love and is perfect for all my everyday uses, especially media – I’m a keen photographer and also getting into film-making. I would have bought a new MacBook, but if I’m honest I couldn’t afford it, and they’ve stopped doing the 17″ screens anyway – big mistake, Apple – but I digress.

Being loathed to get rid of the HP, whose hardware is of a similarly high spec to the MacBook, I’ve decided to use it for a very different purpose, effectively restoring my HP with Linux Mint Tara, which looks like a really elegant system, and and using it to get back into programming with this impressive Python language, so I basically wanted to say thank you to the author for writing these tutorials, and to ask the community for any tips you may have for someone who, while reasonably well-versed with computers generally, is very much out of date on the nuts & bolts side, and basically a beginner where Linux & Python are concerned.

Thank you in advance for any helpful replies.