Python3 + GTK+3 + Glade + Templates = <3

Many software that you use on your Gnome environment could've been developed with Python. Apps like Gnome Music and Gnome Tweaks are some examples.

In this article I'll show you a minimal example in order to give you a foundation for your ideas. Let's go:

Create a basic layout on Glade:

Stuff you need to pay attention to:

• The top level component is a GtkApplicationWindow (you can find it under Toplevels button)
• While it's selected, check the Composite checkbox on the farther right (super important!)
• When you check the Composite checkbox the ID field becomes Class Name. Give it a name and save it, we'll use it soon
• Give the button an ID and save it, we'll use it soon

With the Button selected, switch to the Signals tab:

• Click on the Handler column on the clicked Signal row
• Type the first letter of your button's name
• Accept the suggestion (btnMain_clicked_cb, in my example) and save it, we'll use it soon

And that's it for Glade. Save your .glade file on your project dir.

Create a basic Python skeleton:

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import GLib, Gio, Gtk

import sys


#
# 1. our .glade file (may contain paths)
#
@Gtk.Template.from_file("a.glade")
class AppWindow(Gtk.ApplicationWindow):
    #
    # 2. the GtkApplicationWindow class
    #
    __gtype_name__ = "app_window"

    #
    # 3. the Button name we saved above
    #
    btnMain: Gtk.Button = Gtk.Template.Child()

    #
    # 4. the signal handler name we saved above
    #
    @Gtk.Template.Callback()
    def btnMain_clicked_cb(self, widget, **_kwargs):
        assert self.btnMain == widget
        print(widget.get_label())


class Application(Gtk.Application):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, application_id="dev.monique.Gtk1",
                         flags=Gio.ApplicationFlags.FLAGS_NONE, **kwargs)
        self.window = None

    def do_activate(self):
        self.window = self.window or AppWindow(application=self)
        self.window.present()


if __name__ == '__main__':
    Application().run(sys.argv)

You'll also need to:

pip install PyGObject

It may complain about missing libraries, just read the error output and install the missing dependencies (I had to apt install libcairo2-dev libgirepository1.0-dev)

With this code you'll be able to get started.

Good luck!