Refactored to reduce Glade dependency...

src/core/core_widget.py

@@ -0,0 +1,37 @@
+# Python imports
+
+# Gtk imports
+import gi
+
+gi.require_version('Gtk', '3.0')
+
+from gi.repository import Gtk
+
+# Application imports
+
+
+class CoreWidget(Gtk.Box):
+    def __init__(self):
+        super(CoreWidget, self).__init__()
+
+        self._setup_styling()
+        self._setup_signals()
+        self._load_widgets()
+
+        self.show_all()
+
+
+    def _setup_styling(self):
+        self.set_orientation(1)
+
+    def _setup_signals(self):
+        ...
+
+    def _load_widgets(self):
+        button = Gtk.Button(label="Click Me!")
+        button.connect("clicked", self._hello_world)
+
+        self.add(button)
+
+    def _hello_world(self, widget=None, eve=None):
+        print("Hello, World!")