Changed print to use the function syntax.

docs/examples/lib/gui-gtk3.py

@@ -12,7 +12,7 b' from gi.repository import Gtk'
 
 
 def hello_world(wigdet, data=None):
-    print "Hello World"
+    print("Hello World")
 
 def delete_event(widget, event, data=None):
     return False